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Network Working Group                                         Tim Martin
INTERNET-DRAFT                                      BeThereBeSquare Inc.
Intended status: Standards Track                         Alexey Melnikov
Expires: November 2008                                     Isode Limited
                                                            May 22, 2008



               A Protocol for Remotely Managing Sieve Scripts
                      <draft-martin-managesieve-09.txt>

Status of this Memo

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Copyright Notice

   Copyright (C) The IETF Trust (2008).


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 "sieve" 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.


                           Table of Contents



Status of this Memo  . . . . . . . . . . . . . . . . . . . . . . . .   1
Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   1
1.     Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
1.1.   Changes . . . . . . . . . . . . . . . . . . . . . . . . . . .   3
1.2.   Conventions Used in the Document  . . . . . . . . . . . . . .   4
1.3.   Syntax  . . . . . . . . . . . . . . . . . . . . . . . . . . .   4
1.4.   Response Codes  . . . . . . . . . . . . . . . . . . . . . . .   5
1.5.   Active Script . . . . . . . . . . . . . . . . . . . . . . . .   6
1.6.   Quotas  . . . . . . . . . . . . . . . . . . . . . . . . . . .   7
1.7.   Script Names  . . . . . . . . . . . . . . . . . . . . . . . .   7
1.8.   Capabilities  . . . . . . . . . . . . . . . . . . . . . . . .   7
2.     Commands  . . . . . . . . . . . . . . . . . . . . . . . . . .   8
2.1.   AUTHENTICATE Command  . . . . . . . . . . . . . . . . . . . .   8
2.2.   STARTTLS Command  . . . . . . . . . . . . . . . . . . . . . .  10
2.3.   LOGOUT Command  . . . . . . . . . . . . . . . . . . . . . . .  10
2.4.   CAPABILITY Command  . . . . . . . . . . . . . . . . . . . . .  11
2.5.   HAVESPACE Command . . . . . . . . . . . . . . . . . . . . . .  11
2.6.   PUTSCRIPT Command . . . . . . . . . . . . . . . . . . . . . .  11
2.7.   LISTSCRIPTS Command . . . . . . . . . . . . . . . . . . . . .  13
2.8.   SETACTIVE Command . . . . . . . . . . . . . . . . . . . . . .  13
2.9.   GETSCRIPT Command . . . . . . . . . . . . . . . . . . . . . .  13
2.10.   DELETESCRIPT Command . . . . . . . . . . . . . . . . . . . .  14
3.     Sieve URL Scheme  . . . . . . . . . . . . . . . . . . . . . .  14
4.     Formal Syntax . . . . . . . . . . . . . . . . . . . . . . . .  15
5.     Security Considerations . . . . . . . . . . . . . . . . . . .  18
7.     References  . . . . . . . . . . . . . . . . . . . . . . . . .
7.1.   Normative References  . . . . . . . . . . . . . . . . . . . .
7.2.   Informative References  . . . . . . . . . . . . . . . . . . .
8.     Author's Address  . . . . . . . . . . . . . . . . . . . . . .


1.  Introduction



1.1.  Changes

    [[Note to RFC editor: please delete this section before
    publication]]

    Changes since 08

    - Updated the text describing prohibited Unicode characters in script
      names

    - Clarified that non-synchronizing literals (i.e. {<size>+}CRLF...)
      can only be sent by the client, while synchronizing literals (i.e.
      {<size>}CRLF...) are only sent by the server

    - Various other ABNF fixes

    - Changed DIGEST-MD5 to SCRAM as the mandatory to implement SASL
      mechanism

    - Updated references

    - Other editorial changes

    Changes since 07

    -Fixed examples to match 3028bis - capability names are case
     sensitive, so examples should show "fileinto" instead of
     "FILEINTO", etc.

    -Minor editorial changes

    Changes since 06

    -Clarified meaning of the QUOTA response code

    -Clarified which characters are not allowed in script names
     and the maximum script name length

    -Clarified that the empty list of SASL mechanisms is allowed

    -Clarified that PUTSCRIPT must not store data after anonymous
     authentication

    -Move text about NOTIFY capability into this document

    -Additional examples

    -Updated ABNF, References, Contact information

    Changes since 05

    -More ABNF fixes

    -Added IANA considerations

    -Added/fixed text about AUTHENTICATE.

    -Updated the text om Sieve URLs.

    -Updated and added new examples.

    Changes since 04

    -Updated boilerplate and some references. Added Alexey as co-editor.

    -Minor ABNF fixes

    -Cleaned up terminology (for example, made more consistent with
     SASL)

    -Added more examples, fixed some existing examples

    -Clarified that STARTTLS command is optional

    -Clarified that disabling an active script when there is no script
     active is not an error.

    Changes since 03

    -Add referals and Sieve URLs

    -Lots of spelling/grammer fixes

    -Don't give capabilities after successful STARTTLS. This is because
    it isn't consistant with AUTHENTICATE. There is language specifying
    that a client should re-issue a CAPABILITY command after
    AUTHENTICATE/STARTTLS.

    -Putting a script of length 0 doesn't remove the script. If this
    functionality is desired, the DELETESCRIPT command should be used.

    Changes since 02

    -add BYE response

    -typo on line 588

    -allow ANONYMOUS access for sieve script verification

    -updated SIEVE spec reference

    Changes since 01

    -changed contact info

    Changes since 00

    -added response codes (from ACAP)

    -removed special-ok response from authenticate command (response
    codes obsolete it)

    -changed service name to "sieve"

    -ABNF fixes

    -Alexey's wording changes

    -Eliminated lame PLAIN paragraph

    Changes since PRE

    -dropped synchronized literals. added HAVESPACE command

    -changed capability response syntax. added CAPABILITY command

    -allowed pipelining

    - "sieve" -> "Sieve". Other minor fixes

    -made script names more flexible

    -added starttls support


1.2.  Conventions Used in the 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.


1.3.  Syntax

    This a line oriented protocol much like [IMAP4rev1] or [ACAP]. 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 followed by zero or more strings
    and numbers terminated by a newline.

    All client queries are replied to with either an OK, NO, or BYE
    response. Each response may be followed by a response code (see
    response codes section) and by a string consisting of human readable
    text in the local language. 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 may 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 a
    inactivity timeout resulting in client autologout it MUST be no less
    than 30 minutes.

    <<IANA registration is pending. Current implementations generally
    use port number 2000.>>


1.4.  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.
    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 hierarchy with each level of hierarchy representing
    increasing detail about the error. Clients MUST tolerate additional
    hierarchical response code detail which they don't understand.

    The currently defined response codes are:

    AUTH-TOO-WEAK

    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.

    ENCRYPT-NEEDED

    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.

    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 is near its quota or that the
    user exceeded its quota, but the server supports soft quotas.

    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 "Sieve URL Scheme" section).
    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.

    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, followed by
    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 make sense when returned in a NO/BYE response.


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


1.5.  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 scripts and MUST
    use the SETACTIVE command described below for changing the active
    script or disabling Sieve processing. For example, a user 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.


1.6.  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. Client implementations MUST be able to handle commands
    failing because of quota restrictions.


1.7.  Script Names

    A Sieve script name is a sequence of Unicode characters encoded
    in UTF-8 [UTF-8]. Characters listed in Section 2.3 of [SASLprep]
    are prohibited in Sieve script names.  <<Should we just require
    that all Sieve script names must conform to [SASLprep] output?>>
    Server implementations MAY further restrict the list of allowed
    characters, but they MUST at least allow for US-ASCII DIGIT and
    ALPHA [ABNF] and '-' (hyphen) characters.
    Sieve script names MUST be at least one octet long.  Zero
    octets script name has a special meaning (see SETACTIVE command
    section). Servers MUST allow names of up to 128 Unicode characters
    in length, and MAY allow longer names.


1.8.  Capabilities

    Server capabilities are sent automatically by the server upon a client
    connection, or after successful STARTTLS and AUTHENTICATE (which
    establishes a SASL security layer) commands.
    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

    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

    STARTTLS - If TLS [TLS] is supported by this implementation

    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].

    A server implementation MUST return SIEVE and IMPLEMENTATION
    capabilities.

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

    Example:

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

    <<Add RENAMESCRIPT>>


2.  Commands

    The following commands are valid. Prior to successful authentication
    only the AUTHENTICATE, CAPABILITY, STARTTLS, and LOGOUT commands are
    valid. 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.


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 an 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 rejects 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. I.e. 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.

    If a security layer is negotiated through the SASL authentication
    exchange, it takes effect immediately following the CRLF that
    concludes the 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 which 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, which
    was not obtained from the SASL (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 which alter
    the capabilities list prior to SASL negotiation.
    The capability results MUST include all SASL mechanisms. This is
    done in order to allow client to detect active down-negotiation
    attack.

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

    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, 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 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 1.4 for detailed
    description of the relevant conditions.

    To ensure interoperability, client and server implementations
    of this extension MUST implement the [SCRAM] SASL
    mechanism.


    Implementations MAY advertise the ANONYMOUS SASL mechanism
    [SASL-ANON]. This indicates that the server supports ANONYMOUS SIEVE
    script syntax verification. Only the CAPABILITY, PUTSCRIPT and
    LOGOUT commands are available to the anonymous user. All other
    commands MUST give NO responses. Furthermore the PUTSCRIPT command
    MUST NOT persistently store any data. In this mode a positive
    response to the PUTSCRIPT command indicates that the given script
    does not have any syntax errors.

    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: OK
    C: Authenticate "DIGEST-MD5"
    S: "cmVhbG09ImVsd29vZC5pbm5vc29mdC5jb20iLG5vbmNlPSJPQTZNRzl0
        RVFHbTJoaCIscW9wPSJhdXRoIixhbGdvcml0aG09bWQ1LXNlc3MsY2hh
        cnNldD11dGYtOA=="
    C: "Y2hhcnNldD11dGYtOCx1c2VybmFtZT0iY2hyaXMiLHJlYWxtPSJlbHdvb2
        QuaW5ub3NvZnQuY29tIixub25jZT0iT0E2TUc5dEVRR20yaGgiLG5jPTAw
        MDAwMDAxLGNub25jZT0iT0E2TUhYaDZWcVRyUmsiLGRpZ2VzdC11cmk9Im
        ltYXAvZWx3b29kLmlubm9zb2Z0LmNvbSIscmVzcG9uc2U9ZDM4OGRhZDkw
        ZDRiYmQ3NjBhMTUyMzIxZjIxNDNhZjcscW9wPWF1dGg="
    S: OK (SASL "cnNwYXV0aD1lYTQwZjYwMzM1YzQyN2I1NTI3Yjg0ZGJhYmNkZ
        mZmZA==")

    A slightly different variant of the same authentication exchange:

    S: "IMPLEMENTATION" "Example1 ManageSieved v001"
    S: "SASL" "DIGEST-MD5 GSSAPI"
    S: "SIEVE" "fileinto vacation"
    S: "STARTTLS"
    S: OK
    C: Authenticate "DIGEST-MD5"
    S: {128}
    S: cmVhbG09ImVsd29vZC5pbm5vc29mdC5jb20iLG5vbmNlPSJPQTZNRzl0
       RVFHbTJoaCIscW9wPSJhdXRoIixhbGdvcml0aG09bWQ1LXNlc3MsY2hh
       cnNldD11dGYtOA==
    C: {276+}
    C: Y2hhcnNldD11dGYtOCx1c2VybmFtZT0iY2hyaXMiLHJlYWxtPSJlbHdvb2
       QuaW5ub3NvZnQuY29tIixub25jZT0iT0E2TUc5dEVRR20yaGgiLG5jPTAw
       MDAwMDAxLGNub25jZT0iT0E2TUhYaDZWcVRyUmsiLGRpZ2VzdC11cmk9Im
       ltYXAvZWx3b29kLmlubm9zb2Z0LmNvbSIscmVzcG9uc2U9ZDM4OGRhZDkw
       ZDRiYmQ3NjBhMTUyMzIxZjIxNDNhZjcscW9wPWF1dGg="
    S: {56}
    S: cnNwYXV0aD1lYTQwZjYwMzM1YzQyN2I1NTI3Yjg0ZGJhYmNkZmZmZA==
    C: ""
    S: OK

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

    S: "IMPLEMENTATION" "Example1 ManageSieved v001"
    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: "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>

    The following example demonstrate use of SASL "initial response".
    It also demonstrates that an empty response can be sent as a
    literal:

    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


2.2.  STARTTLS Command

    Support for STARTTLS command in servers is optional. Its
    availability is advertised with "STARTTLS" capability as described
    in section 1.8.

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


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 and terminate the connection. The server MUST ignore
    commands issued by the client after the LOGOUT command.

    Example:

    C: Logout
    S: Ok
    <connection terminated>


2.4.  CAPABILITY Command

    The CAPABILITY command requests the server capabilities as described
    earlier in this document. While the capabilities are sent upon
    connection, they may change during authentication. The client SHOULD
    issue a CAPABILITY command after successful authentication or after
    negotiating a security layer using STARTTLS.


    Example:

    C: CAPABILITY
    S: "IMPLEMENTATION" "Example1 ManageSieved v001"
    S: "SASL" "PLAIN KERBEROS_V4 GSSAPI"
    S: "SIEVE" "fileinto vacation"
    S: "STARTTLS"
    S: OK


2.5.  HAVESPACE Command

    Arguments:
         String - name
         Number - 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. Servers respond with an NO if storing a script
    with that name and size would fail or OK otherwise. Clients SHOULD
    issue this command before attempting to place a script on the
    server.

    Example:

    C: HAVESPACE "myscript" 999999
    S: NO (QUOTA) "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 which 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 syntactic validity.
    If the script fails this test 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 newlines.

    Example:

    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


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.

    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 OK reply.

    If the script does not exist on the server then the server MUST
    reply with a NO response.

    Examples:

    C: Setactive "vacationscript"
    S: Ok

    C: Setactive ""
    S: Ok

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

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


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. Upon
    success a string with the contents of the script is returned
    followed by a 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

    Parameters:
         sieve-name - 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. The server
    MUST NOT allow the client to delete an active script, so the server
    MUST reply with a NO response if attempted. 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 "You may not delete an active script"


3.  Sieve URL Scheme

    URI scheme name: sieve

    Status: permanent

    URI scheme syntax:

      Described using ABNF [ABNF] and ABNF entities from [URI-GEN].

      sieveurl = sieveurl-server / sieveurl-script

      sieveurl-server = "sieve://" authority

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

      scriptname = *pchar

    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 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, the URI
      requests that the client lists available scripts using
      the LISTSCRIPTS command.

    Encoding considerations: The script name, if present,
      is in UTF-8.  Non-US-ASCII UTF-8 octets MUST be percent-encoded as
      described in [URI-GEN].

      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 [RFC XXXX] clients and servers.
      Clients that can store user preferences in protocols such as
      [LDAP] or [ACAP].

    Interoperability considerations:  None.

    Security considerations:  <<None>>.

    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].
    "iana-token" and "extension-data" non-terminal are defined in
    [ACAP].


    Except as noted otherwise, all alphabetic characters are case-
    insensitive. The use of upper or lower case 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 / DQUOTE QUOTED-SPECIALS

    QUOTED-SPECIALS       = DQUOTE / "\"

    SAFE-UTF8-CHAR        = SAFE-CHAR / UTF8-2 / UTF8-3 / UTF8-4 /
                            UTF8-5 / UTF8-6

    UTF8-1                = %x80-BF

    UTF8-2                = %xC0-DF UTF8-1

    UTF8-3                = %xE0-EF 2UTF8-1

    UTF8-4                = %xF0-F7 3UTF8-1

    UTF8-5                = %xF8-FB 4UTF8-1

    UTF8-6                = %xFC-FD 5UTF8-1

    <<Should just reference productions from [UTF-8]?>>

    auth-type             = DQUOTE auth-type-name DQUOTE

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

    command               = command-authenticate / command-logout /
                            command-getscript / command-setactive /
                            command-listscripts / command-deletescript /
                            command-putscript / command-capability /
                            command-havespace / command-starttls

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

    command-capability    = "CAPABILITY" CRLF

    command-deletescript  = "DELETESCRIPT" SP sieve-name CRLF

    command-getscript     = "GETSCRIPT" SP sieve-name CRLF

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

    command-listscripts   = "LISTSCRIPTS" CRLF

    command-logout        = "LOGOUT" CRLF

    command-putscript     = "PUTSCRIPT" SP sieve-name SP string CRLF

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

    command-starttls      = "STARTTLS" CRLF

    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.

    number                = 1*DIGIT
                            ;; A 32-bit unsigned number.
                            ;; (0 <= n < 4,294,967,296)

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

    resp-code             = "AUTH-TOO-WEAK" / "ENCRYPT-NEEDED" /
                            "QUOTA" / resp-code-sasl /
                            resp-code-referral /
                            "TRANSITION-NEEDED" / "TRYLATER" /
                            resp-code-ext

    resp-code-referral    = "REFERRAL" SP sieveurl

    resp-code-sasl        = "SASL" SP string

    resp-code-ext         = iana-token [SP extension-data]
                            ;; unknown response codes MUST be tolerated
                            ;; by the client. "iana-token" and
                            ;; "extension-data" are defined in [ACAP].

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

    response-authenticate = *(string CRLF) (response-oknobye)

    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 "STARTTLS" DQUOTE
                            ;; 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.

    sasl-mechs = string
                 ; space separated list of SASL mechanisms,
                 ; can be empty

    sieve-extensions = string
                 ; space separated list of supported SIEVE extensions,
                 ; can be empty

    response-deletescript = response-oknobye

    response-getscript    = (string 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-ok           = "OK" [SP "(" resp-code ")"]
                            [SP string] CRLF

    response-nobye        = ("NO" / "BYE") [SP "(" resp-code ")"]
                            [SP string] CRLF

    response-oknobye      = response-ok / response-nobye

    response-putscript    = response-oknobye

    response-setactive    = response-oknobye

    response-starttls     = response-oknobye

    sieve-name            = string
                            ;; See Section 1.7 for the full list of
                            ;; prohibited characters.

    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.

    <<Alternatively the whole ABNF can be updated to list places
    where literal-c2s or literal-s2c is allowed>>


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 which 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.


6.  IANA Considerations

    IANA is requested to reserve TCP port number 2000 for use with
    the Manage Sieve protocol described in this document.

    IANA is requested to create a new registry for Manage Sieve
    capabilities. The registration template for Manage Sieve
    capabilities is specified in the next section.
    Manage Sieve protocol capabilities MUST be specified in a standards
    track or IESG approved experimental RFC.

    <<Add a new registry for response codes, as per ABNF comments.>>

    <<Reference to SIEVE URL registration.>>


6.1. Manage Sieve Capability Registration Template

       To: iana@iana.org
       Subject: Manage Sieve Capability Registration

       Please register the following Manage Sieve Capability:

        Capability name:

        Description:

        Relevant publications:

        Person & email address to contact for further information:

        Author/Change controller:


6.2. Registration of Initial Manage Sieve capabilities.

       To: iana@iana.org
       Subject: Manage Sieve Capability Registration

       Please register the following Manage Sieve Capability:

        Capability name: IMPLEMENTATION

        Description: Its value contains name of server
                     implementation and its version.

        Relevant publications: this RFC, section 1.8.

        Person & email address to contact for further information:
         Alexey Melnikov <alexey.melnikov@isode.com>

        Author/Change controller: IESG.


       To: iana@iana.org
       Subject: Manage Sieve Capability Registration

       Please register the following Manage Sieve Capability:

        Capability name: SASL

        Description: Its value contains a space separated
                     list of SASL mechanisms supported by server.

        Relevant publications: this RFC, sections 1.8 and 2.1.

        Person & email address to contact for further information:
         Alexey Melnikov <alexey.melnikov@isode.com>

        Author/Change controller: IESG.


       To: iana@iana.org
       Subject: Manage Sieve Capability Registration

       Please register the following Manage Sieve Capability:

        Capability name: SIEVE

        Description: Its value contains a space separated
                     list of supported SIEVE extensions

        Relevant publications: this RFC, section 1.8.
         Also [SIEVE].

        Person & email address to contact for further information:
         Alexey Melnikov <alexey.melnikov@isode.com>

        Author/Change controller: IESG.


       To: iana@iana.org
       Subject: Manage Sieve Capability Registration

       Please register the following Manage Sieve Capability:

        Capability name: STARTTLS

        Description: This capability is returned if server
                     supports TLS (STARTTLS command).

        Relevant publications: this RFC, sections 1.8 and 2.2.

        Person & email address to contact for further information:
         Alexey Melnikov <alexey.melnikov@isode.com>

        Author/Change controller: IESG.


       To: iana@iana.org
       Subject: Manage Sieve Capability Registration

       Please register the following Manage Sieve Capability:

        Capability name: NOTIFY

        Description: This capability is returned if server
                     supports 'enotify' Sieve extension.

        Relevant publications: this RFC, section 1.8.

        Person & email address to contact for further information:
         Alexey Melnikov <alexey.melnikov@isode.com>

        Author/Change controller: IESG.

7.  References

7.1.  Normative References

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

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

    [ACAP] Newman, Myers, "ACAP -- Application Configuration Access
    Protocol", RFC 2244, Innosoft, Netscape, November 1997.

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

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

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

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

    [SASL-ANON] K. Zeilenga (Ed.), "Anonymous Simple Authentication and
    Security Layer (SASL) Mechanism", RFC 4505, June 2006.

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

    [TLS] Dierks, T. and E. Rescorla, "The Transport Layer Security
    (TLS) Protocol Version 1.1", RFC 4346, April 2006.

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

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

    [NOTIFY] Melnikov, A. (Ed.), Leiba, B. (Ed.), Segmuller, W. and
    T. Martin, "Sieve Extension: Notifications", work in progress,
    draft-ietf-sieve-notify-XX.txt.

    [SCRAM] Menon-Sen, A. and C. Newman, "Salted Challenge Response
    Authentication Mechanism (SCRAM)", work in progress,
    draft-newman-auth-scram-05.txt.


7.2.  Informative References

    [IMAP4rev1] Crispin, M., "Internet Message Access Protocol - Version
    4rev1", RFC 3501, March 2003.

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

    [DIGEST-MD5] Melnikov, A. (Ed.), "Using Digest Authentication as
    a SASL Mechanism", work in progress,
    draft-ietf-sasl-rfc2831bis-XX.txt.

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



8.  Author's Address

    Tim Martin
    BeThereBeSquare Inc.
    672 Haight st.
    San Francisco, CA 94117
    Phone: (510) 260-4175
    EMail: timmartin@alumni.cmu.edu

    Alexey Melnikov
    Isode Ltd.
    5 Castle Business Village
    36 Station Road
    Hampton, Middlesex, TW12 2BX, GB
    Email: alexey.melnikov@isode.com


Intellectual Property

   The IETF takes no position regarding the validity or scope of any
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   to pertain to the implementation or use of the technology described
   in this document or the extent to which any license under such
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   it has made any independent effort to identify any such rights.
   Information on the procedures with respect to rights in RFC
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   copyrights, patents or patent applications, or other proprietary
   rights that may cover technology that may be required to implement
   this standard.  Please address the information to the IETF at
   ietf-ipr@ietf.org.


18.  Full Copyright Statement

   Copyright (C) The IETF Trust (2008).

   This document is subject to the rights, licenses and restrictions
   contained in BCP 78, and except as set forth therein, the authors
   retain all their rights.

   This document and the information contained herein are provided on
   an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE
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   ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS
   FOR A PARTICULAR PURPOSE.

Acknowledgement

   Funding for the RFC Editor function is currently provided by the
   Internet Society.


Appendix A. Acknowledgments

    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 and Jeffrey Hutzelman for help with this document.


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