path: root/docs/[rfc5804] Managing Sieve/rfc5804.txt

Internet Engineering Task Force (IETF)                  A. Melnikov, Ed.
Request for Comments: 5804                                 Isode Limited
Category: Standards Track                                      T. Martin
ISSN: 2070-1721                                    BeThereBeSquare, Inc.
                                                               July 2010


              A Protocol for Remotely Managing Sieve Scripts

Abstract

   Sieve scripts allow users to filter incoming email.  Message stores
   are commonly sealed servers so users cannot log into them, yet users
   must be able to update their scripts on them.  This document
   describes a protocol "ManageSieve" for securely managing Sieve
   scripts on a remote server.  This protocol allows a user to have
   multiple scripts, and also alerts a user to syntactically flawed
   scripts.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc5804.

Copyright Notice

   Copyright (c) 2010 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.




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Table of Contents

   1. Introduction ....................................................3
      1.1. Commands and Responses .....................................3
      1.2. Syntax .....................................................3
      1.3. Response Codes .............................................3
      1.4. Active Script ..............................................6
      1.5. Quotas .....................................................6
      1.6. Script Names ...............................................6
      1.7. Capabilities ...............................................7
      1.8. Transport ..................................................9
      1.9. Conventions Used in This Document .........................10
   2. Commands .......................................................10
      2.1. AUTHENTICATE Command ......................................11
           2.1.1. Use of SASL PLAIN Mechanism over TLS ...............16
      2.2. STARTTLS Command ..........................................16
           2.2.1. Server Identity Check ..............................17
      2.3. LOGOUT Command ............................................20
      2.4. CAPABILITY Command ........................................20
      2.5. HAVESPACE Command .........................................20
      2.6. PUTSCRIPT Command .........................................21
      2.7. LISTSCRIPTS Command .......................................23
      2.8. SETACTIVE Command .........................................24
      2.9. GETSCRIPT Command .........................................25
      2.10. DELETESCRIPT Command .....................................25
      2.11. RENAMESCRIPT Command .....................................26
      2.12. CHECKSCRIPT Command ......................................27
      2.13. NOOP Command .............................................28
      2.14. Recommended Extensions ...................................28
           2.14.1. UNAUTHENTICATE Command ............................28
   3. Sieve URL Scheme ...............................................29
   4. Formal Syntax ..................................................31
   5. Security Considerations ........................................37
   6. IANA Considerations ............................................38
      6.1. ManageSieve Capability Registration Template ..............39
      6.2. Registration of Initial ManageSieve Capabilities ..........39
      6.3. ManageSieve Response Code Registration Template ...........41
      6.4. Registration of Initial ManageSieve Response Codes ........41
   7. Internationalization Considerations ............................46
   8. Acknowledgements ...............................................46
   9. References .....................................................47
      9.1. Normative References ......................................47
      9.2. Informative References ....................................48








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1.  Introduction

1.1.  Commands and Responses

   A ManageSieve connection consists of the establishment of a client/
   server network connection, an initial greeting from the server, and
   client/server interactions.  These client/server interactions consist
   of a client command, server data, and a server completion result
   response.

   All interactions transmitted by client and server are in the form of
   lines, that is, strings that end with a CRLF.  The protocol receiver
   of a ManageSieve client or server is either reading a line or reading
   a sequence of octets with a known count followed by a line.

1.2.  Syntax

   ManageSieve is a line-oriented protocol much like [IMAP] or [ACAP],
   which runs over TCP.  There are three data types: atoms, numbers and
   strings.  Strings may be quoted or literal.  See [ACAP] for detailed
   descriptions of these types.

   Each command consists of an atom (the command name) followed by zero
   or more strings and numbers terminated by CRLF.

   All client queries are replied to with either an OK, NO, or BYE
   response.  Each response may be followed by a response code (see
   Section 1.3) and by a string consisting of human-readable text in the
   local language (as returned by the LANGUAGE capability; see
   Section 1.7), encoded in UTF-8 [UTF-8].  The contents of the string
   SHOULD be shown to the user ,and implementations MUST NOT attempt to
   parse the message for meaning.

   The BYE response SHOULD be used if the server wishes to close the
   connection.  A server may wish to do this because the client was idle
   for too long or there were too many failed authentication attempts.
   This response can be issued at any time and should be immediately
   followed by a server hang-up of the connection.  If a server has an
   inactivity timeout resulting in client autologout, it MUST be no less
   than 30 minutes after successful authentication.  The inactivity
   timeout MAY be less before authentication.

1.3.  Response Codes

   An OK, NO, or BYE response from the server MAY contain a response
   code to describe the event in a more detailed machine-parsable
   fashion.  A response code consists of data inside parentheses in the
   form of an atom, possibly followed by a space and arguments.



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   Response codes are defined when there is a specific action that a
   client can take based upon the additional information.  In order to
   support future extension, the response code is represented as a
   slash-separated (Solidus, %x2F) hierarchy with each level of
   hierarchy representing increasing detail about the error.  Response
   codes MUST NOT start with the Solidus character.  Clients MUST
   tolerate additional hierarchical response code detail that they don't
   understand.  For example, if the client supports the "QUOTA" response
   code, but doesn't understand the "QUOTA/MAXSCRIPTS" response code, it
   should treat "QUOTA/MAXSCRIPTS" as "QUOTA".

   Client implementations MUST tolerate (ignore) response codes that
   they do not recognize.

   The currently defined response codes are the following:

   AUTH-TOO-WEAK

   This response code is returned in the NO or BYE response from an
   AUTHENTICATE command.  It indicates that site security policy forbids
   the use of the requested mechanism for the specified authentication
   identity.

   ENCRYPT-NEEDED

   This response code is returned in the NO or BYE response from an
   AUTHENTICATE command.  It indicates that site security policy
   requires the use of a strong encryption mechanism for the specified
   authentication identity and mechanism.

   QUOTA

   If this response code is returned in the NO/BYE response, it means
   that the command would have placed the user above the site-defined
   quota constraints.  If this response code is returned in the OK
   response, it can mean that the user's storage is near its quota, or
   it can mean that the account exceeded its quota but that the
   condition is being allowed by the server (the server supports
   so-called soft quotas).  The QUOTA response code has two more
   detailed variants: "QUOTA/MAXSCRIPTS" (the maximum number of per-user
   scripts) and "QUOTA/MAXSIZE" (the maximum script size).

   REFERRAL

   This response code may be returned with a BYE result from any
   command, and includes a mandatory parameter that indicates what
   server to access to manage this user's Sieve scripts.  The server
   will be specified by a Sieve URL (see Section 3).  The scriptname



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   portion of the URL MUST NOT be specified.  The client should
   authenticate to the specified server and use it for all further
   commands in the current session.

   SASL

   This response code can occur in the OK response to a successful
   AUTHENTICATE command and includes the optional final server response
   data from the server as specified by [SASL].

   TRANSITION-NEEDED

   This response code occurs in a NO response of an AUTHENTICATE
   command.  It indicates that the user name is valid, but the entry in
   the authentication database needs to be updated in order to permit
   authentication with the specified mechanism.  This is typically done
   by establishing a secure channel using TLS, verifying server identity
   as specified in Section 2.2.1, and finally authenticating once using
   the [PLAIN] authentication mechanism.  The selected mechanism SHOULD
   then work for authentications in subsequent sessions.

   This condition can happen if a user has an entry in a system
   authentication database such as Unix /etc/passwd, but does not have
   credentials suitable for use by the specified mechanism.

   TRYLATER

   A command failed due to a temporary server failure.  The client MAY
   continue using local information and try the command later.  This
   response code only makes sense when returned in a NO/BYE response.

   ACTIVE

   A command failed because it is not allowed on the active script, for
   example, DELETESCRIPT on the active script.  This response code only
   makes sense when returned in a NO/BYE response.

   NONEXISTENT

   A command failed because the referenced script name doesn't exist.
   This response code only makes sense when returned in a NO/BYE
   response.

   ALREADYEXISTS

   A command failed because the referenced script name already exists.
   This response code only makes sense when returned in a NO/BYE
   response.



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   TAG

   This response code name is followed by a string specified in the
   command.  See Section 2.13 for a possible use case.

   WARNINGS

   This response code MAY be returned by the server in the OK response
   (but it might be returned with the NO/BYE response as well) and
   signals the client that even though the script is syntactically
   valid, it might contain errors not intended by the script writer.
   This response code is typically returned in response to PUTSCRIPT
   and/or CHECKSCRIPT commands.  A client seeing such response code
   SHOULD present the returned warning text to the user.

1.4.  Active Script

   A user may have multiple Sieve scripts on the server, yet only one
   script may be used for filtering of incoming messages.  This is the
   active script.  Users may have zero or one active script and MUST use
   the SETACTIVE command described below for changing the active script
   or disabling Sieve processing.  For example, users may have an
   everyday script they normally use and a special script they use when
   they go on vacation.  Users can change which script is being used
   without having to download and upload a script stored somewhere else.

1.5.  Quotas

   Servers SHOULD impose quotas to prevent malicious users from
   overflowing available storage.  If a command would place a user over
   a quota setting, servers that impose such quotas MUST reply with a NO
   response containing the QUOTA response code.  Client implementations
   MUST be able to handle commands failing because of quota
   restrictions.

1.6.  Script Names

   A Sieve script name is a sequence of Unicode characters encoded in
   UTF-8 [UTF-8].  A script name MUST comply with Net-Unicode Definition
   (Section 2 of [NET-UNICODE]), with the additional restriction of
   prohibiting the following Unicode characters:

   o  0000-001F; [CONTROL CHARACTERS]

   o  007F; DELETE

   o  0080-009F; [CONTROL CHARACTERS]




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   o  2028; LINE SEPARATOR

   o  2029; PARAGRAPH SEPARATOR

   Sieve script names MUST be at least one octet (and hence Unicode
   character) long.  Zero octets script name has a special meaning (see
   Section 2.8).  Servers MUST allow names of up to 128 Unicode
   characters in length (which can take up to 512 bytes when encoded in
   UTF-8, not counting the terminating NUL), and MAY allow longer names.
   A server that receives a script name longer than its internal limit
   MUST reject the corresponding operation, in particular it MUST NOT
   truncate the script name.

1.7.  Capabilities

   Server capabilities are sent automatically by the server upon a
   client connection, or after successful STARTTLS and AUTHENTICATE
   (which establishes a Simple Authentication and Security Layer (SASL))
   commands.  Capabilities may change immediately after a successfully
   completed STARTTLS command, and/or immediately after a successfully
   completed AUTHENTICATE command, and/or after a successfully completed
   UNAUTHENTICATE command (see Section 2.14.1).  Capabilities MUST
   remain static at all other times.

   Clients MAY request the capabilities at a later time by issuing the
   CAPABILITY command described later.  The capabilities consist of a
   series of lines each with one or two strings.  The first string is
   the name of the capability, which is case-insensitive.  The second
   optional string is the value associated with that capability.  Order
   of capabilities is arbitrary, but each capability name can appear at
   most once.

   The following capabilities are defined in this document:

   IMPLEMENTATION - Name of implementation and version.  This capability
   MUST always be returned by the server.

   SASL - List of SASL mechanisms supported by the server, each
   separated by a space.  This list can be empty if and only if STARTTLS
   is also advertised.  This means that the client must negotiate TLS
   encryption with STARTTLS first, at which point the SASL capability
   will list a non-empty list of SASL mechanisms.

   SIEVE - List of space-separated Sieve extensions (as listed in Sieve
   "require" action [SIEVE]) supported by the Sieve engine.  This
   capability MUST always be returned by the server.





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   STARTTLS - If TLS [TLS] is supported by this implementation.  Before
   advertising this capability a server MUST verify to the best of its
   ability that TLS can be successfully negotiated by a client with
   common cipher suites.  Specifically, a server should verify that a
   server certificate has been installed and that the TLS subsystem has
   successfully initialized.  This capability SHOULD NOT be advertised
   once STARTTLS or AUTHENTICATE command completes successfully.  Client
   and server implementations MUST implement the STARTTLS extension.

   MAXREDIRECTS - Specifies the limit on the number of Sieve "redirect"
   actions a script can perform during a single evaluation.  Note that
   this is different from the total number of "redirect" actions a
   script can contain.  The value is a non-negative number represented
   as a ManageSieve string.

   NOTIFY - A space-separated list of URI schema parts for supported
   notification methods.  This capability MUST be specified if the Sieve
   implementation supports the "enotify" extension [NOTIFY].

   LANGUAGE - The language (<Language-Tag> from [RFC5646]) currently
   used for human-readable error messages.  If this capability is not
   returned, the "i-default" [RFC2277] language is assumed.  Note that
   the current language MAY be per-user configurable (i.e., it MAY
   change after authentication).

   OWNER - The canonical name of the logged-in user (SASL "authorization
   identity") encoded in UTF-8.  This capability MUST NOT be returned in
   unauthenticated state and SHOULD be returned once the AUTHENTICATE
   command succeeds.

   VERSION - This capability MUST be returned by servers compliant with
   this document or its successor.  For servers compliant with this
   document, the capability value is the string "1.0".  Lack of this
   capability means that the server predates this specification and thus
   doesn't support the following commands: RENAMESCRIPT, CHECKSCRIPT,
   and NOOP.

   Section 2.14 defines some additional ManageSieve extensions and their
   respective capabilities.

   A server implementation MUST return SIEVE, IMPLEMENTATION, and
   VERSION capabilities.

   A client implementation MUST ignore any listed capabilities that it
   does not understand.






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       Example:

       S: "IMPlemENTATION" "Example1 ManageSieved v001"
       S: "SASl" "DIGEST-MD5 GSSAPI"
       S: "SIeVE" "fileinto vacation"
       S: "StaRTTLS"
       S: "NOTIFY" "xmpp mailto"
       S: "MAXREdIRECTS" "5"
       S: "VERSION" "1.0"
       S: OK

   After successful authentication, this might look like this:

       Example:

       S: "IMPlemENTATION" "Example1 ManageSieved v001"
       S: "SASl" "DIGEST-MD5 GSSAPI"
       S: "SIeVE" "fileinto vacation"
       S: "NOTIFY" "xmpp mailto"
       S: "OWNER" "alexey@example.com"
       S: "MAXREdIRECTS" "5"
       S: "VERSION" "1.0"
       S: OK

1.8.  Transport

   The ManageSieve protocol assumes a reliable data stream such as that
   provided by TCP.  When TCP is used, a ManageSieve server typically
   listens on port 4190.

   Before opening the TCP connection, the ManageSieve client first MUST
   resolve the Domain Name System (DNS) hostname associated with the
   receiving entity and determine the appropriate TCP port for
   communication with the receiving entity.  The process is as follows:

   1.  Attempt to resolve the hostname using a [DNS-SRV] Service of
       "sieve" and a Proto of "tcp" for the target domain (e.g.,
       "example.net"), resulting in resource records such as
       "_sieve._tcp.example.net.".  The result of the SRV lookup, if
       successful, will be one or more combinations of a port and
       hostname; the ManageSieve client MUST resolve the returned
       hostnames to IPv4/IPv6 addresses according to returned SRV record
       weight.  IP addresses from the first successfully resolved
       hostname (with the corresponding port number returned by SRV
       lookup) are used to connect to the server.  If connection using
       one of the IP addresses fails, the next resolved IP address is





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       used to connect.  If connection to all resolved IP addresses
       fails, then the resolution/connect is repeated for the next
       hostname returned by SRV lookup.

   2.  If the SRV lookup fails, the fallback SHOULD be a normal IPv4 or
       IPv6 address record resolution to determine the IP address, where
       the port used is the default ManageSieve port of 4190.

1.9.  Conventions Used in This Document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [KEYWORDS].

   In examples, "C:" and "S:" indicate lines sent by the client and
   server respectively.  Line breaks that do not start a new "C:" or
   "S:" exist for editorial reasons.

   Examples of authentication in this document are using DIGEST-MD5
   [DIGEST-MD5] and GSSAPI [GSSAPI] SASL mechanisms.

2.  Commands

   This section and its subsections describe valid ManageSieve commands.
   Upon initial connection to the server, the client's session is in
   non-authenticated state.  Prior to successful authentication, only
   the AUTHENTICATE, CAPABILITY, STARTTLS, LOGOUT, and NOOP (see Section
   2.13) commands are valid.  ManageSieve extensions MAY define other
   commands that are valid in non-authenticated state.  Servers MUST
   reject all other commands with a NO response.  Clients may pipeline
   commands (send more than one command at a time without waiting for
   completion of the first command).  However, a group of commands sent
   together MUST NOT have an AUTHENTICATE (*), a STARTTLS, or a
   HAVESPACE command anywhere but the last command in the list.

   (*) - The only exception to this rule is when the AUTHENTICATE
   command contains an initial response for a SASL mechanism that allows
   clients to send data first, the mechanism is known to complete in one
   round trip, and the mechanism doesn't negotiate a SASL security
   layer.  Two examples of such SASL mechanisms are PLAIN [PLAIN] and
   EXTERNAL [SASL].










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2.1.  AUTHENTICATE Command

   Arguments:  String - mechanism
               String - initial data (optional)

   The AUTHENTICATE command indicates a SASL [SASL] authentication
   mechanism to the server.  If the server supports the requested
   authentication mechanism, it performs an authentication protocol
   exchange to identify and authenticate the user.  Optionally, it also
   negotiates a security layer for subsequent protocol interactions.  If
   the requested authentication mechanism is not supported, the server
   rejects the AUTHENTICATE command by sending the NO response.

   The authentication protocol exchange consists of a series of server
   challenges and client responses that are specific to the selected
   authentication mechanism.  A server challenge consists of a string
   (quoted or literal) followed by a CRLF.  The contents of the string
   is a base-64 encoding [BASE64] of the SASL data.  A client response
   consists of a string (quoted or literal) with the base-64 encoding of
   the SASL data followed by a CRLF.  If the client wishes to cancel the
   authentication exchange, it issues a string containing a single "*".
   If the server receives such a response, it MUST reject the
   AUTHENTICATE command by sending a NO reply.

   Note that an empty challenge/response is sent as an empty string.  If
   the mechanism dictates that the final response is sent by the server,
   this data MAY be placed within the data portion of the SASL response
   code to save a round trip.

   The optional initial-response argument to the AUTHENTICATE command is
   used to save a round trip when using authentication mechanisms that
   are defined to send no data in the initial challenge.  When the
   initial-response argument is used with such a mechanism, the initial
   empty challenge is not sent to the client and the server uses the
   data in the initial-response argument as if it were sent in response
   to the empty challenge.  If the initial-response argument to the
   AUTHENTICATE command is used with a mechanism that sends data in the
   initial challenge, the server MUST reject the AUTHENTICATE command by
   sending the NO response.

   The service name specified by this protocol's profile of SASL is
   "sieve".

   Reauthentication is not supported by ManageSieve protocol's profile
   of SASL.  That is, after a successfully completed AUTHENTICATE
   command, no more AUTHENTICATE commands may be issued in the same
   session.  After a successful AUTHENTICATE command completes, a server
   MUST reject any further AUTHENTICATE commands with a NO reply.



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   However, note that a server may implement the UNAUTHENTICATE
   extension described in Section 2.14.1.

   If a security layer is negotiated through the SASL authentication
   exchange, it takes effect immediately following the CRLF that
   concludes the successful authentication exchange for the client, and
   the CRLF of the OK response for the server.

   When a security layer takes effect, the ManageSieve protocol is reset
   to the initial state (the state in ManageSieve after a client has
   connected to the server).  The server MUST discard any knowledge
   obtained from the client that was not obtained from the SASL (or TLS)
   negotiation itself.  Likewise, the client MUST discard any knowledge
   obtained from the server, such as the list of ManageSieve extensions,
   that was not obtained from the SASL (and/or TLS) negotiation itself.
   (Note that a client MAY compare the advertised SASL mechanisms before
   and after authentication in order to detect an active down-
   negotiation attack.  See below.)

   Once a SASL security layer is established, the server MUST re-issue
   the capability results, followed by an OK response.  This is
   necessary to protect against man-in-the-middle attacks that alter the
   capabilities list prior to SASL negotiation.  The capability results
   MUST include all SASL mechanisms the server was capable of
   negotiating with that client.  This is done in order to allow the
   client to detect an active down-negotiation attack.  If a user-
   oriented client detects such a down-negotiation attack, it SHOULD
   either notify the user (it MAY give the user the opportunity to
   continue with the ManageSieve session in this case) or close the
   transport connection and indicate that a down-negotiation attack
   might be in progress.  If an automated client detects a down-
   negotiation attack, it SHOULD return or log an error indicating that
   a possible attack might be in progress and/or SHOULD close the
   transport connection.

   When both [TLS] and SASL security layers are in effect, the TLS
   encoding MUST be applied (when sending data) after the SASL encoding.

   Server implementations SHOULD support SASL proxy authentication so
   that an administrator can administer a user's scripts.  Proxy
   authentication is when a user authenticates as herself/himself but
   requests the server to act (authorize) as another user.

   The authorization identity generated by this [SASL] exchange is a
   "simple username" (in the sense defined in [SASLprep]), and both
   client and server MUST use the [SASLprep] profile of the [StringPrep]
   algorithm to prepare these names for transmission or comparison.  If
   preparation of the authorization identity fails or results in an



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   empty string (unless it was transmitted as the empty string), the
   server MUST fail the authentication.

   If an AUTHENTICATE command fails with a NO response, the client MAY
   try another authentication mechanism by issuing another AUTHENTICATE
   command.  In other words, the client may request authentication types
   in decreasing order of preference.

   Note that a failed (NO) response to the AUTHENTICATE command may
   contain one of the following response codes: AUTH-TOO-WEAK, ENCRYPT-
   NEEDED, or TRANSITION-NEEDED.  See Section 1.3 for detailed
   description of the relevant conditions.

   To ensure interoperability, both client and server implementations of
   the ManageSieve protocol MUST implement the SCRAM-SHA-1 [SCRAM] SASL
   mechanism, as well as [PLAIN] over [TLS].

   Note: use of PLAIN over TLS reflects current use of PLAIN over TLS in
   other email-related protocols; however, a longer-term goal is to
   migrate email-related protocols from using PLAIN over TLS to SCRAM-
   SHA-1 mechanism.

   Examples (Note that long lines are folded for readability and are not
   part of protocol exchange):

       S: "IMPLEMENTATION" "Example1 ManageSieved v001"
       S: "SASL" "DIGEST-MD5 GSSAPI"
       S: "SIEVE" "fileinto vacation"
       S: "STARTTLS"
       S: "VERSION" "1.0"
       S: OK
       C: Authenticate "DIGEST-MD5"
       S: "cmVhbG09ImVsd29vZC5pbm5vc29mdC5leGFtcGxlLmNvbSIsbm9uY2U9Ik
          9BNk1HOXRFUUdtMmhoIixxb3A9ImF1dGgiLGFsZ29yaXRobT1tZDUtc2Vz
          cyxjaGFyc2V0PXV0Zi04"
       C: "Y2hhcnNldD11dGYtOCx1c2VybmFtZT0iY2hyaXMiLHJlYWxtPSJlbHdvb2
          QuaW5ub3NvZnQuZXhhbXBsZS5jb20iLG5vbmNlPSJPQTZNRzl0RVFHbTJo
          aCIsbmM9MDAwMDAwMDEsY25vbmNlPSJPQTZNSFhoNlZxVHJSayIsZGlnZX
          N0LXVyaT0ic2lldmUvZWx3b29kLmlubm9zb2Z0LmV4YW1wbGUuY29tIixy
          ZXNwb25zZT1kMzg4ZGFkOTBkNGJiZDc2MGExNTIzMjFmMjE0M2FmNyxxb3
          A9YXV0aA=="
       S: OK (SASL "cnNwYXV0aD1lYTQwZjYwMzM1YzQyN2I1NTI3Yjg0ZGJhYmNkZ
          mZmZA==")








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   A slightly different variant of the same authentication exchange is:

       S: "IMPLEMENTATION" "Example1 ManageSieved v001"
       S: "SASL" "DIGEST-MD5 GSSAPI"
       S: "SIEVE" "fileinto vacation"
       S: "VERSION" "1.0"
       S: "STARTTLS"
       S: OK
       C: Authenticate "DIGEST-MD5"
       S: {136}
       S: cmVhbG09ImVsd29vZC5pbm5vc29mdC5leGFtcGxlLmNvbSIsbm9uY2U9Ik
          9BNk1HOXRFUUdtMmhoIixxb3A9ImF1dGgiLGFsZ29yaXRobT1tZDUtc2Vz
          cyxjaGFyc2V0PXV0Zi04
       C: {300+}
       C: Y2hhcnNldD11dGYtOCx1c2VybmFtZT0iY2hyaXMiLHJlYWxtPSJlbHdvb2
          QuaW5ub3NvZnQuZXhhbXBsZS5jb20iLG5vbmNlPSJPQTZNRzl0RVFHbTJo
          aCIsbmM9MDAwMDAwMDEsY25vbmNlPSJPQTZNSFhoNlZxVHJSayIsZGlnZX
          N0LXVyaT0ic2lldmUvZWx3b29kLmlubm9zb2Z0LmV4YW1wbGUuY29tIixy
          ZXNwb25zZT1kMzg4ZGFkOTBkNGJiZDc2MGExNTIzMjFmMjE0M2FmNyxxb3
          A9YXV0aA==
       S: {56}
       S: cnNwYXV0aD1lYTQwZjYwMzM1YzQyN2I1NTI3Yjg0ZGJhYmNkZmZmZA==
       C: ""
       S: OK



























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   Another example demonstrating use of SASL PLAIN mechanism under TLS
   follows.  This example also demonstrate use of SASL "initial
   response" (the second parameter to the Authenticate command):

       S: "IMPLEMENTATION" "Example1 ManageSieved v001"
       S: "VERSION" "1.0"
       S: "SASL" ""
       S: "SIEVE" "fileinto vacation"
       S: "STARTTLS"
       S: OK
       C: STARTTLS
       S: OK
       <TLS negotiation, further commands are under TLS layer>
       S: "IMPLEMENTATION" "Example1 ManageSieved v001"
       S: "VERSION" "1.0"
       S: "SASL" "PLAIN"
       S: "SIEVE" "fileinto vacation"
       S: OK
       C: Authenticate "PLAIN" "QJIrweAPyo6Q1T9xu"
       S: NO
       C: Authenticate "PLAIN" "QJIrweAPyo6Q1T9xz"
       S: NO
       C: Authenticate "PLAIN" "QJIrweAPyo6Q1T9xy"
       S: BYE "Too many failed authentication attempts"
       <Server closes connection>


























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   The following example demonstrates use of SASL "initial response".
   It also demonstrates that an empty response can be sent as a literal
   and that negotiating a SASL security layer results in the server
   re-issuing server capabilities:

       C: AUTHENTICATE "GSSAPI" {1488+}
       C: YIIE[...1480 octets here ...]dA==
       S: {208}
       S: YIGZBgkqhkiG9xIBAgICAG+BiTCBhqADAgEFoQMCAQ+iejB4oAMCARKic
          [...114 octets here ...]
          /yzpAy9p+Y0LanLskOTvMc0MnjgAa4YEr3eJ6
       C: {0+}
       C:
       S: {44}
       S: BQQF/wAMAAwAAAAAYRGFAo6W0vIHti8i1UXODgEAEAA=
       C: {44+}
       C: BQQE/wAMAAwAAAAAIsT1iv9UkZApw471iXt6cwEAAAE=
       S: OK
       <Further commands/responses are under SASL security layer>
       S: "IMPLEMENTATION" "Example1 ManageSieved v001"
       S: "VERSION" "1.0"
       S: "SASL" "PLAIN DIGEST-MD5 GSSAPI"
       S: "SIEVE" "fileinto vacation"
       S: "LANGUAGE" "ru"
       S: "MAXREDIRECTS" "3"
       S: ok

2.1.1.  Use of SASL PLAIN Mechanism over TLS

   This section is normative for ManageSieve client implementations that
   support SASL [PLAIN] over [TLS].

   If a ManageSieve client is willing to use SASL PLAIN over TLS to
   authenticate to the ManageSieve server, the client MUST verify the
   server identity (see Section 2.2.1).  If the server identity can't be
   verified (e.g., the server has not provided any certificate, or if
   the certificate verification fails), the client MUST NOT attempt to
   authenticate using the SASL PLAIN mechanism.

2.2.  STARTTLS Command

   Support for STARTTLS command in servers is optional.  Its
   availability is advertised with "STARTTLS" capability as described in
   Section 1.7.

   The STARTTLS command requests commencement of a TLS [TLS]
   negotiation.  The negotiation begins immediately after the CRLF in
   the OK response.  After a client issues a STARTTLS command, it MUST



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   NOT issue further commands until a server response is seen and the
   TLS negotiation is complete.

   The STARTTLS command is only valid in non-authenticated state.  The
   server remains in non-authenticated state, even if client credentials
   are supplied during the TLS negotiation.  The SASL [SASL] EXTERNAL
   mechanism MAY be used to authenticate once TLS client credentials are
   successfully exchanged, but servers supporting the STARTTLS command
   are not required to support the EXTERNAL mechanism.

   After the TLS layer is established, the server MUST re-issue the
   capability results, followed by an OK response.  This is necessary to
   protect against man-in-the-middle attacks that alter the capabilities
   list prior to STARTTLS.  This capability result MUST NOT include the
   STARTTLS capability.

   The client MUST discard cached capability information and replace it
   with the new information.  The server MAY advertise different
   capabilities after STARTTLS.

       Example:

       C: StartTls
       S: oK
       <TLS negotiation, further commands are under TLS layer>
       S: "IMPLEMENTATION" "Example1 ManageSieved v001"
       S: "SASL" "PLAIN DIGEST-MD5 GSSAPI"
       S: "SIEVE" "fileinto vacation"
       S: "VERSION" "1.0"
       S: "LANGUAGE" "fr"
       S: ok

2.2.1.  Server Identity Check

   During the TLS negotiation, the ManageSieve client MUST check its
   understanding of the server hostname/IP address against the server's
   identity as presented in the server Certificate message, in order to
   prevent man-in-the-middle attacks.  In this section, the client's
   understanding of the server's identity is called the "reference
   identity".

   Checking is performed according to the following rules:

   o  If the reference identity is a hostname:

      1.  If a subjectAltName extension of the SRVName [X509-SRV],
          dNSName [X509] (in that order of preference) type is present
          in the server's certificate, then it SHOULD be used as the



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          source of the server's identity.  Matching is performed as
          described in Section 2.2.1.1, with the exception that no
          wildcard matching is allowed for SRVName type.  If the
          certificate contains multiple names (e.g., more than one
          dNSName field), then a match with any one of the fields is
          considered acceptable.

      2.  The client MAY use other types of subjectAltName for
          performing comparison.

      3.  The server's identity MAY also be verified by comparing the
          reference identity to the Common Name (CN) [RFC4519] value in
          the leaf Relative Distinguished Name (RDN) of the subjectName
          field of the server's certificate.  This comparison is
          performed using the rules for comparison of DNS names in
          Section 2.2.1.1, below.  Although the use of the Common Name
          value is existing practice, it is deprecated, and
          Certification Authorities are encouraged to provide
          subjectAltName values instead.  Note that the TLS
          implementation may represent DNs in certificates according to
          X.500 or other conventions.  For example, some X.500
          implementations order the RDNs in a DN using a left-to-right
          (most significant to least significant) convention instead of
          LDAP's right-to-left convention.

   o  When the reference identity is an IP address, the iPAddress
      subjectAltName SHOULD be used by the client for comparison.  The
      comparison is performed as described in Section 2.2.1.2.

   If the server identity check fails, user-oriented clients SHOULD
   either notify the user (clients MAY give the user the opportunity to
   continue with the ManageSieve session in this case) or close the
   transport connection and indicate that the server's identity is
   suspect.  Automated clients SHOULD return or log an error indicating
   that the server's identity is suspect and/or SHOULD close the
   transport connection.  Automated clients MAY provide a configuration
   setting that disables this check, but MUST provide a setting that
   enables it.

   Beyond the server identity check described in this section, clients
   should be prepared to do further checking to ensure that the server
   is authorized to provide the service it is requested to provide.  The
   client may need to make use of local policy information in making
   this determination.







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2.2.1.1.  Comparison of DNS Names

   If the reference identity is an internationalized domain name,
   conforming implementations MUST convert it to the ASCII Compatible
   Encoding (ACE) format as specified in Section 4 of RFC 3490 [RFC3490]
   before comparison with subjectAltName values of type dNSName.
   Specifically, conforming implementations MUST perform the conversion
   operation specified in Section 4 of [RFC3490] as follows:

   o  in step 1, the domain name SHALL be considered a "stored string";

   o  in step 3, set the flag called "UseSTD3ASCIIRules";

   o  in step 4, process each label with the "ToASCII" operation; and

   o  in step 5, change all label separators to U+002E (full stop).

   After performing the "to-ASCII" conversion, the DNS labels and names
   MUST be compared for equality according to the rules specified in
   Section 3 of [RFC3490]; i.e., once all label separators are replaced
   with U+002E (dot) they are compared in the case-insensitive manner.

   The '*' (ASCII 42) wildcard character is allowed in subjectAltName
   values of type dNSName, and then only as the left-most (least
   significant) DNS label in that value.  This wildcard matches any
   left-most DNS label in the server name.  That is, the subject
   *.example.com matches the server names a.example.com and
   b.example.com, but does not match example.com or a.b.example.com.

2.2.1.2.  Comparison of IP Addresses

   When the reference identity is an IP address, the identity MUST be
   converted to the "network byte order" octet string representation
   [RFC791][RFC2460].  For IP Version 4, as specified in RFC 791, the
   octet string will contain exactly four octets.  For IP Version 6, as
   specified in RFC 2460, the octet string will contain exactly sixteen
   octets.  This octet string is then compared against subjectAltName
   values of type iPAddress.  A match occurs if the reference identity
   octet string and value octet strings are identical.

2.2.1.3.  Comparison of Other subjectName Types

   Client implementations MAY support matching against subjectAltName
   values of other types as described in other documents.







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2.3.  LOGOUT Command

   The client sends the LOGOUT command when it is finished with a
   connection and wishes to terminate it.  The server MUST reply with an
   OK response.  The server MUST ignore commands issued by the client
   after the LOGOUT command.

   The client SHOULD wait for the OK response before closing the
   connection.  This avoids the TCP connection going into the TIME_WAIT
   state on the server.  In order to avoid going into the TIME_WAIT TCP
   state, the server MAY wait for a short while for the client to close
   the TCP connection first.  Whether or not the server waits for the
   client to close the connection, it MUST then close the connection
   itself.

       Example:

       C: Logout
       S: Ok
       <connection is terminated>

2.4.  CAPABILITY Command

   The CAPABILITY command requests the server capabilities as described
   earlier in this document.  It has no parameters.

       Example:

       C: CAPABILITY
       S: "IMPLEMENTATION" "Example1 ManageSieved v001"
       S: "VERSION" "1.0"
       S: "SASL" "PLAIN SCRAM-SHA-1 GSSAPI"
       S: "SIEVE" "fileinto vacation"
       S: "STARTTLS"
       S: OK

2.5.  HAVESPACE Command

   Arguments:  String - name
               Number - script size

   The HAVESPACE command is used to query the server for available
   space.  Clients specify the name they wish to save the script as and
   its size in octets.  Both parameters can be used by the server to see
   if the script with the specified name and size is within a user's
   quota(s).  For example, the server MAY use the script name to check
   if a script would be replaced or a new one would be created.  Servers
   respond with a NO if storing a script with that name and size would



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   fail or OK otherwise.  Clients SHOULD issue this command before
   attempting to place a script on the server.

   Note that the OK response from the HAVESPACE command does not
   constitute a guarantee of success as server disk space conditions
   could change between the client issuing the HAVESPACE and the client
   issuing the PUTSCRIPT commands.  A QUOTA response code (see
   Section 1.3) remains a possible (albeit unlikely) response to a
   subsequent PUTSCRIPT with the same name and size.

       Example:

       C: HAVESPACE "myscript" 999999
       S: NO (QUOTA/MAXSIZE) "Quota exceeded"

       C: HAVESPACE "foobar" 435
       S: OK

2.6.  PUTSCRIPT Command

   Arguments:  String - Script name
               String - Script content

   The PUTSCRIPT command is used by the client to submit a Sieve script
   to the server.

   If the script already exists, upon success the old script will be
   overwritten.  The old script MUST NOT be overwritten if PUTSCRIPT
   fails in any way.  A script of zero length SHOULD be disallowed.

   This command places the script on the server.  It does not affect
   whether the script is processed on incoming mail, unless it replaces
   the script that is already active.  The SETACTIVE command is used to
   mark a script as active.

   When submitting large scripts, clients SHOULD use the HAVESPACE
   command beforehand to query if the server is willing to accept a
   script of that size.

   The server MUST check the submitted script for validity, which
   includes checking that the script complies with the Sieve grammar
   [SIEVE] and that all Sieve extensions mentioned in the script's
   "require" statement(s) are supported by the Sieve interpreter.  (Note
   that if the Sieve interpreter supports the Sieve "ihave" extension
   [I-HAVE], any unrecognized/unsupported extension mentioned in the
   "ihave" test MUST NOT cause the validation failure.)  Other checks
   such as validating the supplied command arguments for each command
   MAY be performed.  Essentially, the performed validation SHOULD be



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   the same as performed when compiling the script for execution.
   Implementations that use a binary representation to store compiled
   scripts can extend the validation to a full compilation, in order to
   avoid validating uploaded scripts multiple times.

   If the script fails the validation, the server MUST reply with a NO
   response.  Any script that fails the validity test MUST NOT be stored
   on the server.  The message given with a NO response MUST be human
   readable and SHOULD contain a specific error message giving the line
   number of the first error.  Implementors should strive to produce
   helpful error messages similar to those given by programming language
   compilers.  Client implementations should note that this may be a
   multiline literal string with more than one error message separated
   by CRLFs.  The human-readable message is in the language returned in
   the latest LANGUAGE capability (or in "i-default"; see Section 1.7),
   encoded in UTF-8 [UTF-8].

   An OK response MAY contain the WARNINGS response code.  In such a
   case the human-readable message that follows the OK response SHOULD
   contain a specific warning message (or messages) giving the line
   number(s) in the script that might contain errors not intended by the
   script writer.  The human-readable message is in the language
   returned in the latest LANGUAGE capability (or in "i-default"; see
   Section 1.7), encoded in UTF-8 [UTF-8].  A client seeing such a
   response code SHOULD present the message to the user.


























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       Examples:

       C: Putscript "foo" {31+}
       C: #comment
       C: InvalidSieveCommand
       C:
       S: NO "line 2: Syntax error"

       C: Putscript "mysievescript" {110+}
       C: require ["fileinto"];
       C:
       C: if envelope :contains "to" "tmartin+sent" {
       C:   fileinto "INBOX.sent";
       C: }
       S: OK

       C: Putscript "myforwards" {190+}
       C: redirect "111@example.net";
       C:
       C: if size :under 10k {
       C:     redirect "mobile@cell.example.com";
       C: }
       C:
       C: if envelope :contains "to" "tmartin+lists" {
       C:     redirect "lists@groups.example.com";
       C: }
       S: OK (WARNINGS) "line 8: server redirect action
               limit is 2, this redirect might be ignored"

2.7.  LISTSCRIPTS Command

   This command lists the scripts the user has on the server.  Upon
   success, a list of CRLF-separated script names (each represented as a
   quoted or literal string) is returned followed by an OK response.  If
   there exists an active script, the atom ACTIVE is appended to the
   corresponding script name.  The atom ACTIVE MUST NOT appear on more
   than one response line.














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       Example:

       C: Listscripts
       S: "summer_script"
       S: "vacation_script"
       S: {13}
       S: clever"script
       S: "main_script" ACTIVE
       S: OK

       C: listscripts
       S: "summer_script"
       S: "main_script" active
       S: OK

2.8.  SETACTIVE Command

   Arguments:  String - script name

   This command sets a script active.  If the script name is the empty
   string (i.e., ""), then any active script is disabled.  Disabling an
   active script when there is no script active is not an error and MUST
   result in an OK reply.

   If the script does not exist on the server, then the server MUST
   reply with a NO response.  Such a reply SHOULD contain the
   NONEXISTENT response code.

       Examples:

       C: Setactive "vacationscript"
       S: Ok

       C: Setactive ""
       S: Ok

       C: Setactive "baz"
       S: No (NONEXISTENT) "There is no script by that name"

       C: Setactive "baz"
       S: No (NONEXISTENT) {31}
       S: There is no script by that name









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2.9.  GETSCRIPT Command

   Arguments:  String - script name

   This command gets the contents of the specified script.  If the
   script does not exist, the server MUST reply with a NO response.
   Such a reply SHOULD contain the NONEXISTENT response code.

   Upon success, a string with the contents of the script is returned
   followed by an OK response.

       Example:

       C: Getscript "myscript"
       S: {54}
       S: #this is my wonderful script
       S: reject "I reject all";
       S:
       S: OK

2.10.  DELETESCRIPT Command

   Arguments:  String - script name

   This command is used to delete a user's Sieve script.  Servers MUST
   reply with a NO response if the script does not exist.  Such
   responses SHOULD include the NONEXISTENT response code.

   The server MUST NOT allow the client to delete an active script, so
   the server MUST reply with a NO response if attempted.  Such a
   response SHOULD contain the ACTIVE response code.  If a client wishes
   to delete an active script, it should use the SETACTIVE command to
   disable the script first.

       Example:

       C: Deletescript "foo"
       S: Ok

       C: Deletescript "baz"
       S: No (ACTIVE) "You may not delete an active script"










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2.11.  RENAMESCRIPT Command

   Arguments:  String - Old Script name
               String - New Script name

   This command is used to rename a user's Sieve script.  Servers MUST
   reply with a NO response if the old script does not exist (in which
   case the NONEXISTENT response code SHOULD be included), or a script
   with the new name already exists (in which case the ALREADYEXISTS
   response code SHOULD be included).  Renaming the active script is
   allowed; the renamed script remains active.

       Example:

       C: Renamescript "foo" "bar"
       S: Ok

       C: Renamescript "baz" "bar"
       S: No "bar already exists"

   If the server doesn't support the RENAMESCRIPT command, the client
   can emulate it by performing the following steps:

   1.  List available scripts with LISTSCRIPTS.  If the script with the
       new script name exists, then the client should ask the user
       whether to abort the operation, to replace the script (by issuing
       the DELETESCRIPT <newname> after that), or to choose a different
       name.

   2.  Download the old script with GETSCRIPT <oldname>.

   3.  Upload the old script with the new name: PUTSCRIPT <newname>.

   4.  If the old script was active (as reported by LISTSCRIPTS in step
       1), then make the new script active: SETACTIVE <newname>.

   5.  Delete the old script: DELETESCRIPT <oldname>.

   Note that these steps don't describe how to handle various other
   error conditions (for example, NO response containing QUOTA response
   code in step 3).  Error handling is left as an exercise for the
   reader.









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2.12.  CHECKSCRIPT Command

   Arguments:  String - Script content

   The CHECKSCRIPT command is used by the client to verify Sieve script
   validity without storing the script on the server.

   The server MUST check the submitted script for syntactic validity,
   which includes checking that all Sieve extensions mentioned in Sieve
   script "require" statement(s) are supported by the Sieve interpreter.
   (Note that if the Sieve interpreter supports the Sieve "ihave"
   extension [I-HAVE], any unrecognized/unsupported extension mentioned
   in the "ihave" test MUST NOT cause the syntactic validation failure.)
   If the script fails this test, the server MUST reply with a NO
   response.  The message given with a NO response MUST be human
   readable and SHOULD contain a specific error message giving the line
   number of the first error.  Implementors should strive to produce
   helpful error messages similar to those given by programming language
   compilers.  Client implementations should note that this may be a
   multiline literal string with more than one error message separated
   by CRLFs.  The human-readable message is in the language returned in
   the latest LANGUAGE capability (or in "i-default"; see Section 1.7),
   encoded in UTF-8 [UTF-8].

       Examples:

       C: CheckScript {31+}
       C: #comment
       C: InvalidSieveCommand
       C:
       S: NO "line 2: Syntax error"

   A ManageSieve server supporting this command MUST NOT check if the
   script will put the current user over its quota limit.

   An OK response MAY contain the WARNINGS response code.  In such a
   case, the human-readable message that follows the OK response SHOULD
   contain a specific warning message (or messages) giving the line
   number(s) in the script that might contain errors not intended by the
   script writer.  The human-readable message is in the language
   returned in the latest LANGUAGE capability (or in "i-default"; see
   Section 1.7), encoded in UTF-8 [UTF-8].  A client seeing such a
   response code SHOULD present the message to the user.








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2.13.  NOOP Command

   Arguments:  String - tag to echo back (optional)

   The NOOP command does nothing, beyond returning a response to the
   client.  It may be used by clients for protocol re-synchronization or
   to reset any inactivity auto-logout timer on the server.

   The response to the NOOP command is always OK, followed by the TAG
   response code together with the supplied string.  If no string was
   supplied in the NOOP command, the TAG response code MUST NOT be
   included.

       Examples:

       C: NOOP
       S: OK "NOOP completed"

       C: NOOP "STARTTLS-SYNC-42"
       S: OK (TAG {16}
       S: STARTTLS-SYNC-42) "Done"

2.14.  Recommended Extensions

   The UNAUTHENTICATE extension (advertised as the "UNAUTHENTICATE"
   capability with no parameters) defines a new UNAUTHENTICATE command,
   which allows a client to return the server to non-authenticated
   state.  Support for this extension is RECOMMENDED.

2.14.1.  UNAUTHENTICATE Command

   The UNAUTHENTICATE command returns the server to the
   non-authenticated state.  It doesn't affect any previously
   established TLS [TLS] or SASL (Section 2.1) security layer.

   The UNAUTHENTICATE command is only valid in authenticated state.  If
   issued in a wrong state, the server MUST reject it with a NO
   response.

   The UNAUTHENTICATE command has no parameters.

   When issued in the authenticated state, the UNAUTHENTICATE command
   MUST NOT fail (i.e., it must never return anything other than OK or
   BYE).







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3.  Sieve URL Scheme

   URI scheme name: sieve

   Status: permanent

   URI scheme syntax: Described using ABNF [ABNF].  Some ABNF
   productions not defined below are from [URI-GEN].

         sieveurl = sieveurl-server / sieveurl-list-scripts /
                    sieveurl-script

         sieveurl-server = "sieve://" authority

         sieveurl-list-scripts = "sieve://" authority ["/"]

         sieveurl-script = "sieve://" authority "/"
                           [owner "/"] scriptname

         authority = <defined in [URI-GEN]>

         owner         = *ochar
                         ;; %-encoded version of [SASL] authorization
                         ;; identity (script owner) or "userid".
                         ;;
                         ;; Empty owner is used to reference
                         ;; global scripts.
                         ;;
                         ;; Note that ASCII characters such as " ", ";",
                         ;; "&", "=", "/" and "?" must be %-encoded
                         ;; as per rule specified in [URI-GEN].

         scriptname    = 1*ochar
                         ;; %-encoded version of UTF-8 representation
                         ;; of the script name.
                         ;; Note that ASCII characters such as " ", ";",
                         ;; "&", "=", "/" and "?" must be %-encoded
                         ;; as per rule specified in [URI-GEN].

         ochar         = unreserved / pct-encoded / sub-delims-sh /
                         ":" / "@"
                         ;; Same as [URI-GEN] 'pchar',
                         ;; but without ";", "&" and "=".

         unreserved = <defined in [URI-GEN]>

         pct-encoded = <defined in [URI-GEN]>




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         sub-delims-sh = "!" / "$" / "'" / "(" / ")" /
                         "*" / "+" / ","
                         ;; Same as [URI-GEN] sub-delims,
                         ;; but without ";", "&" and "=".

   URI scheme semantics:

      A Sieve URL identifies a Sieve server or a Sieve script on a Sieve
      server.  The latter form is associated with the application/sieve
      MIME type defined in [SIEVE].  There is no MIME type associated
      with the former form of Sieve URI.

      The server form is used in the REFERRAL response code (see Section
      1.3) in order to designate another server where the client should
      perform its operations.

      The script form allows to retrieve (GETSCRIPT), update
      (PUTSCRIPT), delete (DELETESCRIPT), or activate (SETACTIVE) the
      named script; however, the most typical action would be to
      retrieve the script.  If the script name is empty (omitted), the
      URI requests that the client lists available scripts using the
      LISTSCRIPTS command.

   Encoding considerations:

      The script name and/or the owner, if present, is in UTF-8.  Non--
      US-ASCII UTF-8 octets MUST be percent-encoded as described in
      [URI-GEN].  US-ASCII characters such as " " (space), ";", "&",
      "=", "/" and "?"  MUST be %-encoded as described in [URI-GEN].
      Note that "&" and "?" are in this list in order to allow for
      future extensions.

      Note that the empty owner (e.g., sieve://example.com//script) is
      different from the missing owner (e.g.,
      sieve://example.com/script) and is reserved for referencing global
      scripts.

      The user name (in the "authority" part), if present, is in UTF-8.
      Non-US-ASCII UTF-8 octets MUST be percent-encoded as described in
      [URI-GEN].

   Applications/protocols that use this URI scheme name:
   ManageSieve [RFC5804] clients and servers.  Clients that can store
   user preferences in protocols such as [LDAP] or [ACAP].

   Interoperability considerations: None.





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   Security considerations:
   The <scriptname> part of a ManageSieve URL might potentially disclose
   some confidential information about the author of the script or,
   depending on a ManageSieve implementation, about configuration of the
   mail system.  The latter might be used to prepare for a more complex
   attack on the mail system.

   Clients resolving ManageSieve URLs that wish to achieve data
   confidentiality and/or integrity SHOULD use the STARTTLS command (if
   supported by the server) before starting authentication, or use a
   SASL mechanism, such as GSSAPI, that provides a confidentiality
   security layer.

   Contact: Alexey Melnikov <alexey.melnikov@isode.com>

   Author/Change controller: IESG.

   References: This document and RFC 5228 [SIEVE].

4.  Formal Syntax

   The following syntax specification uses the Augmented Backus-Naur
   Form (BNF) notation as specified in [ABNF].  This uses the ABNF core
   rules as specified in Appendix A of the ABNF specification [ABNF].
   "UTF8-2", "UTF8-3", and "UTF8-4" non-terminal are defined in [UTF-8].

   Except as noted otherwise, all alphabetic characters are case-
   insensitive.  The use of upper- or lowercase characters to define
   token strings is for editorial clarity only.  Implementations MUST
   accept these strings in a case-insensitive fashion.

    SAFE-CHAR             = %x01-09 / %x0B-0C / %x0E-21 / %x23-5B /
                            %x5D-7F
                            ;; any TEXT-CHAR except QUOTED-SPECIALS

    QUOTED-CHAR           = SAFE-UTF8-CHAR / "\" QUOTED-SPECIALS

    QUOTED-SPECIALS       = DQUOTE / "\"

    SAFE-UTF8-CHAR        = SAFE-CHAR / UTF8-2 / UTF8-3 / UTF8-4
                            ;; <UTF8-2>, <UTF8-3>, and <UTF8-4>
                            ;; are defined in [UTF-8].

    ATOM-CHAR             = "!" / %x23-27 / %x2A-5B / %x5D-7A / %x7C-7E
                            ;; Any CHAR except ATOM-SPECIALS

    ATOM-SPECIALS         = "(" / ")" / "{" / SP / CTL / QUOTED-SPECIALS




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    NZDIGIT               = %x31-39
                            ;; 1-9

    atom                  = 1*1024ATOM-CHAR

    iana-token            = atom
                            ;; MUST be registered with IANA

    auth-type             = DQUOTE auth-type-name DQUOTE

    auth-type-name        = iana-token
                            ;; as defined in SASL [SASL]

    command               = (command-any / command-auth /
                             command-nonauth) CRLF
                            ;; Modal based on state

    command-any           = command-capability / command-logout /
                            command-noop
                            ;; Valid in all states

    command-auth          = command-getscript / command-setactive /
                            command-listscripts / command-deletescript /
                            command-putscript / command-checkscript /
                            command-havespace /
                            command-renamescript /
                            command-unauthenticate
                            ;; Valid only in Authenticated state

    command-nonauth       = command-authenticate / command-starttls
                            ;; Valid only when in Non-Authenticated
                            ;; state

    command-authenticate  = "AUTHENTICATE" SP auth-type [SP string]
                            *(CRLF string)

    command-capability    = "CAPABILITY"

    command-deletescript  = "DELETESCRIPT" SP sieve-name

    command-getscript     = "GETSCRIPT" SP sieve-name

    command-havespace     = "HAVESPACE" SP sieve-name SP number

    command-listscripts   = "LISTSCRIPTS"

    command-noop          = "NOOP" [SP string]




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    command-logout        = "LOGOUT"

    command-putscript     = "PUTSCRIPT" SP sieve-name SP sieve-script

    command-checkscript   = "CHECKSCRIPT" SP sieve-script

    sieve-script          = string

    command-renamescript  = "RENAMESCRIPT" SP old-sieve-name SP
                            new-sieve-name

    old-sieve-name        = sieve-name

    new-sieve-name        = sieve-name

    command-setactive     = "SETACTIVE" SP active-sieve-name

    command-starttls      = "STARTTLS"

    command-unauthenticate= "UNAUTHENTICATE"

    extend-token          = atom
                            ;; MUST be defined by a Standards Track or
                            ;; IESG-approved experimental protocol
                            ;; extension

    extension-data        = extension-item *(SP extension-item)

    extension-item        = extend-token / string / number /
                            "(" [extension-data] ")"

    literal-c2s           = "{" number "+}" CRLF *OCTET
                            ;; The number represents the number of
                            ;; octets.
                            ;; This type of literal can only be sent
                            ;; from the client to the server.

    literal-s2c           = "{" number "}" CRLF *OCTET
                            ;; Almost identical to literal-c2s,
                            ;; but with no '+' character.
                            ;; The number represents the number of
                            ;; octets.
                            ;; This type of literal can only be sent
                            ;; from the server to the client.







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    number                = (NZDIGIT *DIGIT) / "0"
                            ;; A 32-bit unsigned number
                            ;; with no extra leading zeros.
                            ;; (0 <= n < 4,294,967,296)

    number-str            = string
                            ;; <number> encoded as a <string>.

    quoted                = DQUOTE *1024QUOTED-CHAR DQUOTE
                            ;; limited to 1024 octets between the <">s

    resp-code             = "AUTH-TOO-WEAK" / "ENCRYPT-NEEDED" / "QUOTA"
                            ["/" ("MAXSCRIPTS" / "MAXSIZE")] /
                            resp-code-sasl /
                            resp-code-referral /
                            "TRANSITION-NEEDED" / "TRYLATER" /
                            "ACTIVE" / "NONEXISTENT" /
                            "ALREADYEXISTS" / "WARNINGS" /
                            "TAG" SP string /
                            resp-code-ext

    resp-code-referral    = "REFERRAL" SP sieveurl

    resp-code-sasl        = "SASL" SP string

    resp-code-name        = iana-token
                            ;; The response code name is hierarchical,
                            ;; separated by '/'.
                            ;; The response code name MUST NOT start
                            ;; with '/'.

    resp-code-ext         = resp-code-name [SP extension-data]
                            ;; unknown response codes MUST be tolerated
                            ;; by the client.

    response              = response-authenticate /
                            response-logout /
                            response-getscript /
                            response-setactive /
                            response-listscripts /
                            response-deletescript /
                            response-putscript /
                            response-checkscript /
                            response-capability /
                            response-havespace /
                            response-starttls /
                            response-renamescript /
                            response-noop /



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                            response-unauthenticate

    response-authenticate = *(string CRLF)
                            ((response-ok [response-capability]) /
                             response-nobye)
                            ;; <response-capability> is REQUIRED if a
                            ;; SASL security layer was negotiated and
                            ;; MUST be omitted otherwise.

    response-capability   = *(single-capability) response-oknobye

    single-capability     = capability-name [SP string] CRLF

    capability-name       = string

                            ;; Note that literal-s2c is allowed.

    initial-capabilities  = DQUOTE "IMPLEMENTATION" DQUOTE SP string /
                            DQUOTE "SASL" DQUOTE SP sasl-mechs /
                            DQUOTE "SIEVE" DQUOTE SP sieve-extensions /
                            DQUOTE "MAXREDIRECTS" DQUOTE SP number-str /
                            DQUOTE "NOTIFY" DQUOTE SP notify-mechs /
                            DQUOTE "STARTTLS" DQUOTE /
                            DQUOTE "LANGUAGE" DQUOTE SP language /
                            DQUOTE "VERSION" DQUOTE SP version /
                            DQUOTE "OWNER" DQUOTE SP string
                            ;; Each capability conforms to
                            ;; the syntax for single-capability.
                            ;; Also, note that the capability name
                            ;; can be returned as either literal-s2c
                            ;; or quoted, even though only "quoted"
                            ;; string is shown above.

    version = ( DQUOTE "1.0" DQUOTE ) / version-ext

    version-ext = DQUOTE ver-major "." ver-minor DQUOTE
                 ; Future versions specified in updates
                 ; to this document.  An increment to
                 ; the ver-major means a backward-incompatible
                 ; change to the protocol, e.g., "3.5" (ver-major "3")
                 ; is not backward-compatible with any "2.X" version.
                 ; Any version "Z.W" MUST be backward compatible
                 ; with any version "Z.Q", where Q < W.
                 ; For example, version "2.4" is backward compatible
                 ; with version "2.0", "2.1", "2.2", and "2.3".

    ver-major = number




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    ver-minor = number

    sasl-mechs = string
                 ; Space-separated list of SASL mechanisms,
                 ; each SASL mechanism name complies with rules
                 ; specified in [SASL].
                 ; Can be empty.

    sieve-extensions = string
                 ; Space-separated list of supported SIEVE extensions.
                 ; Can be empty.

    language     = string
                 ; Contains <Language-Tag> from [RFC5646].


    notify-mechs = string
                 ; Space-separated list of URI schema parts
                 ; for supported notification [NOTIFY] methods.
                 ; MUST NOT be empty.

    response-deletescript = response-oknobye

    response-getscript    = (sieve-script CRLF response-ok) /
                            response-nobye

    response-havespace    = response-oknobye

    response-listscripts  = *(sieve-name [SP "ACTIVE"] CRLF)
                            response-oknobye
                            ;; ACTIVE may only occur with one sieve-name

    response-logout       = response-oknobye

    response-unauthenticate= response-oknobye
                             ;; "NO" response can only be returned when
                             ;; the command is issued in a wrong state
                             ;; or has a wrong number of parameters

    response-ok           = "OK" [SP "(" resp-code ")"]
                            [SP string] CRLF
                            ;; The string contains human-readable text
                            ;; encoded as UTF-8.

    response-nobye        = ("NO" / "BYE") [SP "(" resp-code ")"]
                            [SP string] CRLF
                            ;; The string contains human-readable text
                            ;; encoded as UTF-8.



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    response-oknobye      = response-ok / response-nobye

    response-noop         = response-ok

    response-putscript    = response-oknobye

    response-checkscript  = response-oknobye

    response-renamescript = response-oknobye

    response-setactive    = response-oknobye

    response-starttls     = (response-ok response-capability) /
                            response-nobye

    sieve-name            = string
                            ;; See Section 1.6 for the full list of
                            ;; prohibited characters.
                            ;; Empty string is not allowed.

    active-sieve-name     = string
                            ;; See Section 1.6 for the full list of
                            ;; prohibited characters.
                            ;; This is similar to <sieve-name>, but
                            ;; empty string is allowed and has a special
                            ;; meaning.

    string                = quoted / literal-c2s / literal-s2c
                            ;; literal-c2s is only allowed when sent
                            ;; from the client to the server.
                            ;; literal-s2c is only allowed when sent
                            ;; from the server to the client.
                            ;; quoted is allowed in either direction.

5.  Security Considerations

   The AUTHENTICATE command uses SASL [SASL] to provide authentication
   and authorization services.  Integrity and privacy services can be
   provided by [SASL] and/or [TLS].  When a SASL mechanism is used, the
   security considerations for that mechanism apply.

   This protocol's transactions are susceptible to passive observers or
   man-in-the-middle attacks that alter the data, unless the optional
   encryption and integrity services of the SASL (via the AUTHENTICATE
   command) and/or [TLS] (via the STARTTLS command) are enabled, or an
   external security mechanism is used for protection.  It may be useful
   to allow configuration of both clients and servers to refuse to
   transfer sensitive information in the absence of strong encryption.



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   If an implementation supports SASL mechanisms that are vulnerable to
   passive eavesdropping attacks (such as [PLAIN]), then the
   implementation MUST support at least one configuration where these
   SASL mechanisms are not advertised or used without the presence of an
   external security layer such as [TLS].

   Some response codes returned on failed AUTHENTICATE command may
   disclose whether or not the username is valid (e.g., TRANSITION-
   NEEDED), so server implementations SHOULD provide the ability to
   disable these features (or make them not conditional on a per-user
   basis) for sites concerned about such disclosure.  In the case of
   ENCRYPT-NEEDED, if it is applied to all identities then no extra
   information is disclosed, but if it is applied on a per-user basis it
   can disclose information.

   A compromised or malicious server can use the TRANSITION-NEEDED
   response code to force the client that is configured to use a
   mechanism that does not disclose the user's password to the server
   (e.g., Kerberos), to send the bare password to the server.  Clients
   SHOULD have the ability to disable the password transition feature,
   or disclose that risk to the user and offer the user an option of how
   to proceed.

6.  IANA Considerations

   IANA has reserved TCP port number 4190 for use with the ManageSieve
   protocol described in this document.

   IANA has registered the "sieve" URI scheme defined in Section 3 of
   this document.

   IANA has registered "sieve" in the "GSSAPI/Kerberos/SASL Service
   Names" registry.

   IANA has created a new registry for ManageSieve capabilities.  The
   registration template for ManageSieve capabilities is specified in
   Section 6.1.  ManageSieve protocol capabilities MUST be specified in
   a Standards-Track or IESG-approved Experimental RFC.

   IANA has created a new registry for ManageSieve response codes.  The
   registration template for ManageSieve response codes is specified in
   Section 6.3.  ManageSieve protocol response codes MUST be specified
   in a Standards-Track or IESG-approved Experimental RFC.








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6.1.  ManageSieve Capability Registration Template

   To: iana@iana.org
   Subject: ManageSieve Capability Registration

   Please register the following ManageSieve capability:

   Capability name:
   Description:
   Relevant publications:
   Person & email address to contact for further information:
   Author/Change controller:

6.2.  Registration of Initial ManageSieve Capabilities

   To: iana@iana.org
   Subject: ManageSieve Capability Registration

   Please register the following ManageSieve capabilities:

   Capability name:  IMPLEMENTATION
   Description:   Its value contains the name of the server
                  implementation and its version.
   Relevant publications:  this RFC, Section 1.7.
   Person & email address to contact for further information:
                  Alexey Melnikov <alexey.melnikov@isode.com>
   Author/Change controller:  IESG.

   Capability name:  SASL
   Description:   Its value contains a space-separated list of SASL
                  mechanisms supported by the server.
   Relevant publications:  this RFC, Sections 1.7 and 2.1.
   Person & email address to contact for further information:
                  Alexey Melnikov <alexey.melnikov@isode.com>
   Author/Change controller:  IESG.

   Capability name:  SIEVE
   Description:   Its value contains a space-separated list of supported
                  SIEVE extensions.
   Relevant publications:  this RFC, Section 1.7.  Also [SIEVE].
   Person & email address to contact for further information:
                  Alexey Melnikov <alexey.melnikov@isode.com>
   Author/Change controller:  IESG.








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   Capability name:  STARTTLS
   Description:   This capability is returned if the server supports TLS
                  (STARTTLS command).
   Relevant publications:  this RFC, Sections 1.7 and 2.2.
   Person & email address to contact for further information:
                  Alexey Melnikov <alexey.melnikov@isode.com>
   Author/Change controller:  IESG.

   Capability name:  NOTIFY
   Description:   This capability is returned if the server supports the
                  'enotify' [NOTIFY] Sieve extension.
   Relevant publications:  this RFC, Section 1.7.
   Person & email address to contact for further information:
                  Alexey Melnikov <alexey.melnikov@isode.com>
   Author/Change controller:  IESG.

   Capability name:  MAXREDIRECTS
   Description:   This capability returns the limit on the number of
                  Sieve "redirect" actions a script can perform during a
                  single evaluation.  The value is a non-negative number
                  represented as a ManageSieve string.
   Relevant publications:  this RFC, Section 1.7.
   Person & email address to contact for further information:
                  Alexey Melnikov <alexey.melnikov@isode.com>
   Author/Change controller:  IESG.

   Capability name:  LANGUAGE
   Description:   The language (<Language-Tag> from [RFC5646]) currently
                  used for human-readable error messages.
   Relevant publications:  this RFC, Section 1.7.
   Person & email address to contact for further information:
                  Alexey Melnikov <alexey.melnikov@isode.com>
   Author/Change controller:  IESG.

   Capability name:  OWNER
   Description:   Its value contains the UTF-8-encoded name of the
                  currently logged-in user ("authorization identity"
                  according to RFC 4422).
   Relevant publications:  this RFC, Section 1.7.
   Person & email address to contact for further information:
                  Alexey Melnikov <alexey.melnikov@isode.com>
   Author/Change controller:  IESG.









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   Capability name:  VERSION
   Description:   This capability is returned if the server is compliant
                  with RFC 5804; i.e., that it supports RENAMESCRIPT,
                  CHECKSCRIPT, and NOOP commands.
   Relevant publications:  this RFC, Sections 2.11, 2.12, and 2.13.
   Person & email address to contact for further information:
                  Alexey Melnikov <alexey.melnikov@isode.com>
   Author/Change controller:  IESG.

6.3.  ManageSieve Response Code Registration Template

   To: iana@iana.org
   Subject: ManageSieve Response Code Registration

   Please register the following ManageSieve response code:

      Response Code:
      Arguments (use ABNF to specify syntax, or the word NONE if none
      can be specified):
      Purpose:
      Published Specification(s):
      Person & email address to contact for further information:
      Author/Change controller:

6.4.  Registration of Initial ManageSieve Response Codes

   To: iana@iana.org
   Subject: ManageSieve Response Code Registration

   Please register the following ManageSieve response codes:

   Response Code: AUTH-TOO-WEAK
   Arguments (use ABNF to specify syntax, or the word NONE if none can
   be specified):  NONE
   Purpose:       This response code is returned in the NO response from
                  an AUTHENTICATE command.  It indicates that site
                  security policy forbids the use of the requested
                  mechanism for the specified authentication identity.
   Published Specification(s):  [RFC5804]
   Person & email address to contact for further information:
                  Alexey Melnikov <alexey.melnikov@isode.com>
   Author/Change controller:  IESG.









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   Response Code: ENCRYPT-NEEDED
   Arguments (use ABNF to specify syntax, or the word NONE if none can
   be specified):  NONE
   Purpose:       This response code is returned in the NO response from
                  an AUTHENTICATE command.  It indicates that site
                  security policy requires the use of a strong
                  encryption mechanism for the specified authentication
                  identity and mechanism.
   Published Specification(s):  [RFC5804]
   Person & email address to contact for further information:
                  Alexey Melnikov <alexey.melnikov@isode.com>
   Author/Change controller:  IESG.

   Response Code: QUOTA
   Arguments (use ABNF to specify syntax, or the word NONE if none can
   be specified):  NONE
   Purpose:       If this response code is returned in the NO/BYE
                  response, it means that the command would have placed
                  the user above the site-defined quota constraints.  If
                  this response code is returned in the OK response, it
                  can mean that the user is near its quota or that the
                  user exceeded its quota, but the server supports soft
                  quotas.
   Published Specification(s):  [RFC5804]
   Person & email address to contact for further information:
                  Alexey Melnikov <alexey.melnikov@isode.com>
   Author/Change controller:  IESG.

   Response Code: QUOTA/MAXSCRIPTS
   Arguments (use ABNF to specify syntax, or the word NONE if none can
   be specified):  NONE
   Purpose:       If this response code is returned in the NO/BYE
                  response, it means that the command would have placed
                  the user above the site-defined limit on the number of
                  Sieve scripts.  If this response code is returned in
                  the OK response, it can mean that the user is near its
                  quota or that the user exceeded its quota, but the
                  server supports soft quotas.  This response code is a
                  more specific version of the QUOTA response code.
   Published Specification(s):  [RFC5804]
   Person & email address to contact for further information:
                  Alexey Melnikov <alexey.melnikov@isode.com>
   Author/Change controller:  IESG.








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   Response Code: QUOTA/MAXSIZE
   Arguments (use ABNF to specify syntax, or the word NONE if none can
   be specified):  NONE
   Purpose:       If this response code is returned in the NO/BYE
                  response, it means that the command would have placed
                  the user above the site-defined maximum script size.
                  If this response code is returned in the OK response,
                  it can mean that the user is near its quota or that
                  the user exceeded its quota, but the server supports
                  soft quotas.  This response code is a more specific
                  version of the QUOTA response code.
   Published Specification(s):  [RFC5804]
   Person & email address to contact for further information:
                  Alexey Melnikov <alexey.melnikov@isode.com>
   Author/Change controller:  IESG.

   Response Code: REFERRAL
   Arguments (use ABNF to specify syntax, or the word NONE if none can
   be specified):  <sieveurl>
   Purpose:       This response code may be returned with a BYE result
                  from any command, and includes a mandatory parameter
                  that indicates what server to access to manage this
                  user's Sieve scripts.  The server will be specified by
                  a Sieve URL (see Section 3).  The scriptname portion
                  of the URL MUST NOT be specified.  The client should
                  authenticate to the specified server and use it for
                  all further commands in the current session.
   Published Specification(s):  [RFC5804]
   Person & email address to contact for further information:
                  Alexey Melnikov <alexey.melnikov@isode.com>
   Author/Change controller:  IESG.

   Response Code: SASL
   Arguments (use ABNF to specify syntax, or the word NONE if none can
   be specified):  <string>
   Purpose:       This response code can occur in the OK response to a
                  successful AUTHENTICATE command and includes the
                  optional final server response data from the server as
                  specified by [SASL].
   Published Specification(s):  [RFC5804]
   Person & email address to contact for further information:
                  Alexey Melnikov <alexey.melnikov@isode.com>
   Author/Change controller:  IESG.








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   Response Code: TRANSITION-NEEDED
   Arguments (use ABNF to specify syntax, or the word NONE if none can
   be specified):  NONE
   Purpose:       This response code occurs in a NO response of an
                  AUTHENTICATE command.  It indicates that the user name
                  is valid, but the entry in the authentication database
                  needs to be updated in order to permit authentication
                  with the specified mechanism.  This is typically done
                  by establishing a secure channel using TLS, followed
                  by authenticating once using the [PLAIN]
                  authentication mechanism.  The selected mechanism
                  SHOULD then work for authentications in subsequent
                  sessions.
   Published Specification(s):  [RFC5804]
   Person & email address to contact for further information:
                  Alexey Melnikov <alexey.melnikov@isode.com>
   Author/Change controller:  IESG.

   Response Code: TRYLATER
   Arguments (use ABNF to specify syntax, or the word NONE if none can
   be specified):  NONE
   Purpose:       A command failed due to a temporary server failure.
                  The client MAY continue using local information and
                  try the command later.  This response code only make
                  sense when returned in a NO/BYE response.
   Published Specification(s):  [RFC5804]
   Person & email address to contact for further information:
                  Alexey Melnikov <alexey.melnikov@isode.com>
   Author/Change controller:  IESG.

   Response Code: ACTIVE
   Arguments (use ABNF to specify syntax, or the word NONE if none can
   be specified):  NONE
   Purpose:       A command failed because it is not allowed on the
                  active script, for example, DELETESCRIPT on the active
                  script.  This response code only makes sense when
                  returned in a NO/BYE response.
   Published Specification(s):  [RFC5804]
   Person & email address to contact for further information:
                  Alexey Melnikov <alexey.melnikov@isode.com>
   Author/Change controller:  IESG.










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   Response Code: NONEXISTENT
   Arguments (use ABNF to specify syntax, or the word NONE if none can
   be specified):  NONE
   Purpose:       A command failed because the referenced script name
                  doesn't exist.  This response code only makes sense
                  when returned in a NO/BYE response.
   Published Specification(s):  [RFC5804]
   Person & email address to contact for further information:
                  Alexey Melnikov <alexey.melnikov@isode.com>
   Author/Change controller:  IESG.

   Response Code: ALREADYEXISTS
   Arguments (use ABNF to specify syntax, or the word NONE if none can
   be specified):  NONE
   Purpose:       A command failed because the referenced script name
                  already exists.  This response code only makes sense
                  when returned in a NO/BYE response.
   Published Specification(s):  [RFC5804]
   Person & email address to contact for further information:
                  Alexey Melnikov <alexey.melnikov@isode.com>
   Author/Change controller:  IESG.

   Response Code: WARNINGS
   Arguments (use ABNF to specify syntax, or the word NONE if none can
   be specified):  NONE
   Purpose:       This response code MAY be returned by the server in
                  the OK response (but it might be returned with the NO/
                  BYE response as well) and signals the client that even
                  though the script is syntactically valid, it might
                  contain errors not intended by the script writer.
   Published Specification(s):  [RFC5804]
   Person & email address to contact for further information:
                  Alexey Melnikov <alexey.melnikov@isode.com>
   Author/Change controller:  IESG.

   Response Code: TAG
   Arguments (use ABNF to specify syntax, or the word NONE if none can
   be specified):  string
   Purpose:       This response code name is followed by a string
                  specified in the command that caused this response.
                  It is typically used for client state synchronization.
   Published Specification(s):  [RFC5804]
   Person & email address to contact for further information:
                  Alexey Melnikov <alexey.melnikov@isode.com>
   Author/Change controller:  IESG.






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7.  Internationalization Considerations

   The LANGUAGE capability (see Section 1.7) allows a client to discover
   the current language used in all human-readable responses that might
   be returned at the end of any OK/NO/BYE response.  Human-readable
   text in OK responses typically doesn't need to be shown to the user,
   unless it is returned in response to a PUTSCRIPT or CHECKSCRIPT
   command that also contains the WARNINGS response code (Section 1.3).
   Human-readable text from NO/BYE responses is intended be shown to the
   user, unless the client can automatically handle failure of the
   command that caused such a response.  Clients SHOULD use response
   codes (Section 1.3) for automatic error handling.  Response codes MAY
   also be used by the client to present error messages in a language
   understood by the user, for example, if the LANGUAGE capability
   doesn't return a language understood by the user.

   Note that the human-readable text from OK (WARNINGS) or NO/BYE
   responses for PUTSCRIPT/CHECKSCRIPT commands is intended for advanced
   users that understand Sieve language.  Such advanced users are often
   sophisticated enough to be able to handle whatever language the
   server is using, even if it is not their preferred language, and will
   want to see error/warning text no matter what language the server
   puts it in.

   A client that generates Sieve script automatically, for example, if
   the script is generated without user intervention or from a UI that
   presents an abstract list of conditions and corresponding actions,
   SHOULD NOT present warning/error messages to the user, because the
   user might not even be aware that the client is using Sieve
   underneath.  However, if the client has a debugging mode, such
   warnings/errors SHOULD be available in the debugging mode.

   Note that this document doesn't provide a way to modify the currently
   used language.  It is expected that a future extension will address
   that.

8.  Acknowledgements

   Thanks to Simon Josefsson, Larry Greenfield, Allen Johnson, Chris
   Newman, Lyndon Nerenberg, Tim Showalter, Sarah Robeson, Walter Wong,
   Barry Leiba, Arnt Gulbrandsen, Stephan Bosch, Ken Murchison, Phil
   Pennock, Ned Freed, Jeffrey Hutzelman, Mark E. Mallett, Dilyan
   Palauzov, Dave Cridland, Aaron Stone, Robert Burrell Donkin, Patrick
   Ben Koetter, Bjoern Hoehrmann, Martin Duerst, Pasi Eronen, Magnus
   Westerlund, Tim Polk, and Julien Coloos for help with this document.
   Special thank you to Phil Pennock for providing text for the NOOP
   command, as well as finding various bugs in the document.




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9.  References

9.1.  Normative References

   [ABNF]         Crocker, D. and P. Overell, "Augmented BNF for Syntax
                  Specifications: ABNF", STD 68, RFC 5234, January 2008.

   [ACAP]         Newman, C. and J. Myers, "ACAP -- Application
                  Configuration Access Protocol", RFC 2244, November
                  1997.

   [BASE64]       Josefsson, S., "The Base16, Base32, and Base64 Data
                  Encodings", RFC 4648, October 2006.

   [DNS-SRV]      Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR
                  for specifying the location of services (DNS SRV)",
                  RFC 2782, February 2000.

   [KEYWORDS]     Bradner, S., "Key words for use in RFCs to Indicate
                  Requirement Levels", BCP 14, RFC 2119, March 1997.

   [NET-UNICODE]  Klensin, J. and M. Padlipsky, "Unicode Format for
                  Network Interchange", RFC 5198, March 2008.

   [NOTIFY]       Melnikov, A., Leiba, B., Segmuller, W., and T. Martin,
                  "Sieve Email Filtering: Extension for Notifications",
                  RFC 5435, January 2009.

   [RFC2277]      Alvestrand, H., "IETF Policy on Character Sets and
                  Languages", BCP 18, RFC 2277, January 1998.

   [RFC2460]      Deering, S. and R. Hinden, "Internet Protocol, Version
                  6 (IPv6) Specification", RFC 2460, December 1998.

   [RFC3490]      Faltstrom, P., Hoffman, P., and A. Costello,
                  "Internationalizing Domain Names in Applications
                  (IDNA)", RFC 3490, March 2003.

   [RFC4519]      Sciberras, A., "Lightweight Directory Access Protocol
                  (LDAP): Schema for User Applications", RFC 4519, June
                  2006.

   [RFC5646]      Phillips, A. and M. Davis, "Tags for Identifying
                  Languages", BCP 47, RFC 5646, September 2009.

   [RFC791]       Postel, J., "Internet Protocol", STD 5, RFC 791,
                  September 1981.




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   [SASL]         Melnikov, A. and K. Zeilenga, "Simple Authentication
                  and Security Layer (SASL)", RFC 4422, June 2006.

   [SASLprep]     Zeilenga, K., "SASLprep: Stringprep Profile for User
                  Names and Passwords", RFC 4013, February 2005.

   [SCRAM]        Menon-Sen, A., Melnikov, A., Newman, C., and N.
                  Williams, "Salted Challenge Response Authentication
                  Mechanism (SCRAM) SASL and GSS-API Mechanisms", RFC
                  5802, July 2010.

   [SIEVE]        Guenther, P. and T. Showalter, "Sieve: An Email
                  Filtering Language", RFC 5228, January 2008.

   [StringPrep]   Hoffman, P. and M. Blanchet, "Preparation of
                  Internationalized Strings ("stringprep")", RFC 3454,
                  December 2002.

   [TLS]          Dierks, T. and E. Rescorla, "The Transport Layer
                  Security (TLS) Protocol Version 1.2", RFC 5246, August
                  2008.

   [URI-GEN]      Berners-Lee, T., Fielding, R., and L. Masinter,
                  "Uniform Resource Identifier (URI): Generic Syntax",
                  STD 66, RFC 3986, January 2005.

   [UTF-8]        Yergeau, F., "UTF-8, a transformation format of ISO
                  10646", STD 63, RFC 3629, November 2003.

   [X509]         Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
                  Housley, R., and W. Polk, "Internet X.509 Public Key
                  Infrastructure Certificate and Certificate Revocation
                  List (CRL) Profile", RFC 5280, May 2008.

   [X509-SRV]     Santesson, S., "Internet X.509 Public Key
                  Infrastructure Subject Alternative Name for Expression
                  of Service Name", RFC 4985, August 2007.

9.2.  Informative References

   [DIGEST-MD5]   Leach, P. and C. Newman, "Using Digest Authentication
                  as a SASL Mechanism", RFC 2831, May 2000.

   [GSSAPI]       Melnikov, A., "The Kerberos V5 ("GSSAPI") Simple
                  Authentication and Security Layer (SASL) Mechanism",
                  RFC 4752, November 2006.





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   [I-HAVE]       Freed, N., "Sieve Email Filtering: Ihave Extension",
                  RFC 5463, March 2009.

   [IMAP]         Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL -
                  VERSION 4rev1", RFC 3501, March 2003.

   [LDAP]         Zeilenga, K., "Lightweight Directory Access Protocol
                  (LDAP): Technical Specification Road Map", RFC 4510,
                  June 2006.

   [PLAIN]        Zeilenga, K., "The PLAIN Simple Authentication and
                  Security Layer (SASL) Mechanism", RFC 4616, August
                  2006.

Authors' Addresses

   Alexey Melnikov (editor)
   Isode Limited
   5 Castle Business Village
   36 Station Road
   Hampton, Middlesex  TW12 2BX
   UK

   EMail: Alexey.Melnikov@isode.com


   Tim Martin
   BeThereBeSquare, Inc.
   672 Haight st.
   San Francisco, CA  94117
   USA

   Phone: +1 510 260-4175
   EMail: timmartin@alumni.cmu.edu

















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