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RFC 3501

 
 
 

INTERNET MESSAGE ACCESS PROTOCOL - VERSION 4rev1

Part 2 of 4, p. 18 to 47
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5.      Operational Considerations

   The following rules are listed here to ensure that all IMAP4rev1
   implementations interoperate properly.

5.1.    Mailbox Naming

   Mailbox names are 7-bit.  Client implementations MUST NOT attempt to
   create 8-bit mailbox names, and SHOULD interpret any 8-bit mailbox
   names returned by LIST or LSUB as UTF-8.  Server implementations
   SHOULD prohibit the creation of 8-bit mailbox names, and SHOULD NOT
   return 8-bit mailbox names in LIST or LSUB.  See section 5.1.3 for
   more information on how to represent non-ASCII mailbox names.

        Note: 8-bit mailbox names were undefined in earlier
        versions of this protocol.  Some sites used a local 8-bit
        character set to represent non-ASCII mailbox names.  Such
        usage is not interoperable, and is now formally deprecated.

   The case-insensitive mailbox name INBOX is a special name reserved to
   mean "the primary mailbox for this user on this server".  The
   interpretation of all other names is implementation-dependent.

   In particular, this specification takes no position on case
   sensitivity in non-INBOX mailbox names.  Some server implementations
   are fully case-sensitive; others preserve case of a newly-created
   name but otherwise are case-insensitive; and yet others coerce names
   to a particular case.  Client implementations MUST interact with any
   of these.  If a server implementation interprets non-INBOX mailbox
   names as case-insensitive, it MUST treat names using the
   international naming convention specially as described in section
   5.1.3.

   There are certain client considerations when creating a new mailbox
   name:

   1)    Any character which is one of the atom-specials (see the Formal
         Syntax) will require that the mailbox name be represented as a
         quoted string or literal.

   2)    CTL and other non-graphic characters are difficult to represent
         in a user interface and are best avoided.

   3)    Although the list-wildcard characters ("%" and "*") are valid
         in a mailbox name, it is difficult to use such mailbox names
         with the LIST and LSUB commands due to the conflict with
         wildcard interpretation.

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   4)    Usually, a character (determined by the server implementation)
         is reserved to delimit levels of hierarchy.

   5)    Two characters, "#" and "&", have meanings by convention, and
         should be avoided except when used in that convention.

5.1.1.  Mailbox Hierarchy Naming

   If it is desired to export hierarchical mailbox names, mailbox names
   MUST be left-to-right hierarchical using a single character to
   separate levels of hierarchy.  The same hierarchy separator character
   is used for all levels of hierarchy within a single name.

5.1.2.  Mailbox Namespace Naming Convention

   By convention, the first hierarchical element of any mailbox name
   which begins with "#" identifies the "namespace" of the remainder of
   the name.  This makes it possible to disambiguate between different
   types of mailbox stores, each of which have their own namespaces.

        For example, implementations which offer access to USENET
        newsgroups MAY use the "#news" namespace to partition the
        USENET newsgroup namespace from that of other mailboxes.
        Thus, the comp.mail.misc newsgroup would have a mailbox
        name of "#news.comp.mail.misc", and the name
        "comp.mail.misc" can refer to a different object (e.g., a
        user's private mailbox).

5.1.3.  Mailbox International Naming Convention

   By convention, international mailbox names in IMAP4rev1 are specified
   using a modified version of the UTF-7 encoding described in [UTF-7].
   Modified UTF-7 may also be usable in servers that implement an
   earlier version of this protocol.

   In modified UTF-7, printable US-ASCII characters, except for "&",
   represent themselves; that is, characters with octet values 0x20-0x25
   and 0x27-0x7e.  The character "&" (0x26) is represented by the
   two-octet sequence "&-".

   All other characters (octet values 0x00-0x1f and 0x7f-0xff) are
   represented in modified BASE64, with a further modification from
   [UTF-7] that "," is used instead of "/".  Modified BASE64 MUST NOT be
   used to represent any printing US-ASCII character which can represent
   itself.

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   "&" is used to shift to modified BASE64 and "-" to shift back to
   US-ASCII.  There is no implicit shift from BASE64 to US-ASCII, and
   null shifts ("-&" while in BASE64; note that "&-" while in US-ASCII
   means "&") are not permitted.  However, all names start in US-ASCII,
   and MUST end in US-ASCII; that is, a name that ends with a non-ASCII
   ISO-10646 character MUST end with a "-").

   The purpose of these modifications is to correct the following
   problems with UTF-7:

      1) UTF-7 uses the "+" character for shifting; this conflicts with
         the common use of "+" in mailbox names, in particular USENET
         newsgroup names.

      2) UTF-7's encoding is BASE64 which uses the "/" character; this
         conflicts with the use of "/" as a popular hierarchy delimiter.

      3) UTF-7 prohibits the unencoded usage of "\"; this conflicts with
         the use of "\" as a popular hierarchy delimiter.

      4) UTF-7 prohibits the unencoded usage of "~"; this conflicts with
         the use of "~" in some servers as a home directory indicator.

      5) UTF-7 permits multiple alternate forms to represent the same
         string; in particular, printable US-ASCII characters can be
         represented in encoded form.

      Although modified UTF-7 is a convention, it establishes certain
      requirements on server handling of any mailbox name with an
      embedded "&" character.  In particular, server implementations
      MUST preserve the exact form of the modified BASE64 portion of a
      modified UTF-7 name and treat that text as case-sensitive, even if
      names are otherwise case-insensitive or case-folded.

      Server implementations SHOULD verify that any mailbox name with an
      embedded "&" character, used as an argument to CREATE, is: in the
      correctly modified UTF-7 syntax, has no superfluous shifts, and
      has no encoding in modified BASE64 of any printing US-ASCII
      character which can represent itself.  However, client
      implementations MUST NOT depend upon the server doing this, and
      SHOULD NOT attempt to create a mailbox name with an embedded "&"
      character unless it complies with the modified UTF-7 syntax.

      Server implementations which export a mail store that does not
      follow the modified UTF-7 convention MUST convert to modified
      UTF-7 any mailbox name that contains either non-ASCII characters
      or the "&" character.

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           For example, here is a mailbox name which mixes English,
           Chinese, and Japanese text:
           ~peter/mail/&U,BTFw-/&ZeVnLIqe-

           For example, the string "&Jjo!" is not a valid mailbox
           name because it does not contain a shift to US-ASCII
           before the "!".  The correct form is "&Jjo-!".  The
           string "&U,BTFw-&ZeVnLIqe-" is not permitted because it
           contains a superfluous shift.  The correct form is
           "&U,BTF2XlZyyKng-".

5.2.    Mailbox Size and Message Status Updates

   At any time, a server can send data that the client did not request.
   Sometimes, such behavior is REQUIRED.  For example, agents other than
   the server MAY add messages to the mailbox (e.g., new message
   delivery), change the flags of the messages in the mailbox (e.g.,
   simultaneous access to the same mailbox by multiple agents), or even
   remove messages from the mailbox.  A server MUST send mailbox size
   updates automatically if a mailbox size change is observed during the
   processing of a command.  A server SHOULD send message flag updates
   automatically, without requiring the client to request such updates
   explicitly.

   Special rules exist for server notification of a client about the
   removal of messages to prevent synchronization errors; see the
   description of the EXPUNGE response for more detail.  In particular,
   it is NOT permitted to send an EXISTS response that would reduce the
   number of messages in the mailbox; only the EXPUNGE response can do
   this.

   Regardless of what implementation decisions a client makes on
   remembering data from the server, a client implementation MUST record
   mailbox size updates.  It MUST NOT assume that any command after the
   initial mailbox selection will return the size of the mailbox.

5.3.    Response when no Command in Progress

   Server implementations are permitted to send an untagged response
   (except for EXPUNGE) while there is no command in progress.  Server
   implementations that send such responses MUST deal with flow control
   considerations.  Specifically, they MUST either (1) verify that the
   size of the data does not exceed the underlying transport's available
   window size, or (2) use non-blocking writes.

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5.4.    Autologout Timer

   If a server has an inactivity autologout timer, the duration of that
   timer MUST be at least 30 minutes.  The receipt of ANY command from
   the client during that interval SHOULD suffice to reset the
   autologout timer.

5.5.    Multiple Commands in Progress

   The client MAY send another command without waiting for the
   completion result response of a command, subject to ambiguity rules
   (see below) and flow control constraints on the underlying data
   stream.  Similarly, a server MAY begin processing another command
   before processing the current command to completion, subject to
   ambiguity rules.  However, any command continuation request responses
   and command continuations MUST be negotiated before any subsequent
   command is initiated.

   The exception is if an ambiguity would result because of a command
   that would affect the results of other commands.  Clients MUST NOT
   send multiple commands without waiting if an ambiguity would result.
   If the server detects a possible ambiguity, it MUST execute commands
   to completion in the order given by the client.

   The most obvious example of ambiguity is when a command would affect
   the results of another command, e.g., a FETCH of a message's flags
   and a STORE of that same message's flags.

   A non-obvious ambiguity occurs with commands that permit an untagged
   EXPUNGE response (commands other than FETCH, STORE, and SEARCH),
   since an untagged EXPUNGE response can invalidate sequence numbers in
   a subsequent command.  This is not a problem for FETCH, STORE, or
   SEARCH commands because servers are prohibited from sending EXPUNGE
   responses while any of those commands are in progress.  Therefore, if
   the client sends any command other than FETCH, STORE, or SEARCH, it
   MUST wait for the completion result response before sending a command
   with message sequence numbers.

        Note: UID FETCH, UID STORE, and UID SEARCH are different
        commands from FETCH, STORE, and SEARCH.  If the client
        sends a UID command, it must wait for a completion result
        response before sending a command with message sequence
        numbers.

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   For example, the following non-waiting command sequences are invalid:

      FETCH + NOOP + STORE
      STORE + COPY + FETCH
      COPY + COPY
      CHECK + FETCH

   The following are examples of valid non-waiting command sequences:

      FETCH + STORE + SEARCH + CHECK
      STORE + COPY + EXPUNGE

      UID SEARCH + UID SEARCH may be valid or invalid as a non-waiting
      command sequence, depending upon whether or not the second UID
      SEARCH contains message sequence numbers.

6.      Client Commands

   IMAP4rev1 commands are described in this section.  Commands are
   organized by the state in which the command is permitted.  Commands
   which are permitted in multiple states are listed in the minimum
   permitted state (for example, commands valid in authenticated and
   selected state are listed in the authenticated state commands).

   Command arguments, identified by "Arguments:" in the command
   descriptions below, are described by function, not by syntax.  The
   precise syntax of command arguments is described in the Formal Syntax
   section.

   Some commands cause specific server responses to be returned; these
   are identified by "Responses:" in the command descriptions below.
   See the response descriptions in the Responses section for
   information on these responses, and the Formal Syntax section for the
   precise syntax of these responses.  It is possible for server data to
   be transmitted as a result of any command.  Thus, commands that do
   not specifically require server data specify "no specific responses
   for this command" instead of "none".

   The "Result:" in the command description refers to the possible
   tagged status responses to a command, and any special interpretation
   of these status responses.

   The state of a connection is only changed by successful commands
   which are documented as changing state.  A rejected command (BAD
   response) never changes the state of the connection or of the
   selected mailbox.  A failed command (NO response) generally does not
   change the state of the connection or of the selected mailbox; the
   exception being the SELECT and EXAMINE commands.

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6.1.    Client Commands - Any State

   The following commands are valid in any state: CAPABILITY, NOOP, and
   LOGOUT.

6.1.1.  CAPABILITY Command

   Arguments:  none

   Responses:  REQUIRED untagged response: CAPABILITY

   Result:     OK - capability completed
               BAD - command unknown or arguments invalid

      The CAPABILITY command requests a listing of capabilities that the
      server supports.  The server MUST send a single untagged
      CAPABILITY response with "IMAP4rev1" as one of the listed
      capabilities before the (tagged) OK response.

      A capability name which begins with "AUTH=" indicates that the
      server supports that particular authentication mechanism.  All
      such names are, by definition, part of this specification.  For
      example, the authorization capability for an experimental
      "blurdybloop" authenticator would be "AUTH=XBLURDYBLOOP" and not
      "XAUTH=BLURDYBLOOP" or "XAUTH=XBLURDYBLOOP".

      Other capability names refer to extensions, revisions, or
      amendments to this specification.  See the documentation of the
      CAPABILITY response for additional information.  No capabilities,
      beyond the base IMAP4rev1 set defined in this specification, are
      enabled without explicit client action to invoke the capability.

      Client and server implementations MUST implement the STARTTLS,
      LOGINDISABLED, and AUTH=PLAIN (described in [IMAP-TLS])
      capabilities.  See the Security Considerations section for
      important information.

      See the section entitled "Client Commands -
      Experimental/Expansion" for information about the form of site or
      implementation-specific capabilities.

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   Example:    C: abcd CAPABILITY
               S: * CAPABILITY IMAP4rev1 STARTTLS AUTH=GSSAPI
               LOGINDISABLED
               S: abcd OK CAPABILITY completed
               C: efgh STARTTLS
               S: efgh OK STARTLS completed
               <TLS negotiation, further commands are under [TLS] layer>
               C: ijkl CAPABILITY
               S: * CAPABILITY IMAP4rev1 AUTH=GSSAPI AUTH=PLAIN
               S: ijkl OK CAPABILITY completed


6.1.2.  NOOP Command

   Arguments:  none

   Responses:  no specific responses for this command (but see below)

   Result:     OK - noop completed
               BAD - command unknown or arguments invalid

      The NOOP command always succeeds.  It does nothing.

      Since any command can return a status update as untagged data, the
      NOOP command can be used as a periodic poll for new messages or
      message status updates during a period of inactivity (this is the
      preferred method to do this).  The NOOP command can also be used
      to reset any inactivity autologout timer on the server.

   Example:    C: a002 NOOP
               S: a002 OK NOOP completed
                  . . .
               C: a047 NOOP
               S: * 22 EXPUNGE
               S: * 23 EXISTS
               S: * 3 RECENT
               S: * 14 FETCH (FLAGS (\Seen \Deleted))
               S: a047 OK NOOP completed

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6.1.3.  LOGOUT Command

   Arguments:  none

   Responses:  REQUIRED untagged response: BYE

   Result:     OK - logout completed
               BAD - command unknown or arguments invalid

      The LOGOUT command informs the server that the client is done with
      the connection.  The server MUST send a BYE untagged response
      before the (tagged) OK response, and then close the network
      connection.

   Example:    C: A023 LOGOUT
               S: * BYE IMAP4rev1 Server logging out
               S: A023 OK LOGOUT completed
               (Server and client then close the connection)

6.2.    Client Commands - Not Authenticated State

   In the not authenticated state, the AUTHENTICATE or LOGIN command
   establishes authentication and enters the authenticated state.  The
   AUTHENTICATE command provides a general mechanism for a variety of
   authentication techniques, privacy protection, and integrity
   checking; whereas the LOGIN command uses a traditional user name and
   plaintext password pair and has no means of establishing privacy
   protection or integrity checking.

   The STARTTLS command is an alternate form of establishing session
   privacy protection and integrity checking, but does not establish
   authentication or enter the authenticated state.

   Server implementations MAY allow access to certain mailboxes without
   establishing authentication.  This can be done by means of the
   ANONYMOUS [SASL] authenticator described in [ANONYMOUS].  An older
   convention is a LOGIN command using the userid "anonymous"; in this
   case, a password is required although the server may choose to accept
   any password.  The restrictions placed on anonymous users are
   implementation-dependent.

   Once authenticated (including as anonymous), it is not possible to
   re-enter not authenticated state.

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   In addition to the universal commands (CAPABILITY, NOOP, and LOGOUT),
   the following commands are valid in the not authenticated state:
   STARTTLS, AUTHENTICATE and LOGIN.  See the Security Considerations
   section for important information about these commands.

6.2.1.  STARTTLS Command

   Arguments:  none

   Responses:  no specific response for this command

   Result:     OK - starttls completed, begin TLS negotiation
               BAD - command unknown or arguments invalid

      A [TLS] negotiation begins immediately after the CRLF at the end
      of the tagged OK response from the server.  Once 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 server remains in the non-authenticated state, even if client
      credentials are supplied during the [TLS] negotiation.  This does
      not preclude an authentication mechanism such as EXTERNAL (defined
      in [SASL]) from using client identity determined by the [TLS]
      negotiation.

      Once [TLS] has been started, the client MUST discard cached
      information about server capabilities and SHOULD re-issue the
      CAPABILITY command.  This is necessary to protect against man-in-
      the-middle attacks which alter the capabilities list prior to
      STARTTLS.  The server MAY advertise different capabilities after
      STARTTLS.

   Example:    C: a001 CAPABILITY
               S: * CAPABILITY IMAP4rev1 STARTTLS LOGINDISABLED
               S: a001 OK CAPABILITY completed
               C: a002 STARTTLS
               S: a002 OK Begin TLS negotiation now
               <TLS negotiation, further commands are under [TLS] layer>
               C: a003 CAPABILITY
               S: * CAPABILITY IMAP4rev1 AUTH=PLAIN
               S: a003 OK CAPABILITY completed
               C: a004 LOGIN joe password
               S: a004 OK LOGIN completed

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6.2.2.  AUTHENTICATE Command

   Arguments:  authentication mechanism name

   Responses:  continuation data can be requested

   Result:     OK - authenticate completed, now in authenticated state
               NO - authenticate failure: unsupported authentication
                    mechanism, credentials rejected
               BAD - command unknown or arguments invalid,
                    authentication exchange cancelled

      The AUTHENTICATE command indicates a [SASL] authentication
      mechanism to the server.  If the server supports the requested
      authentication mechanism, it performs an authentication protocol
      exchange to authenticate and identify the client.  It MAY also
      negotiate an OPTIONAL security layer for subsequent protocol
      interactions.  If the requested authentication mechanism is not
      supported, the server SHOULD reject the AUTHENTICATE command by
      sending a tagged NO response.

      The AUTHENTICATE command does not support the optional "initial
      response" feature of [SASL].  Section 5.1 of [SASL] specifies how
      to handle an authentication mechanism which uses an initial
      response.

      The service name specified by this protocol's profile of [SASL] is
      "imap".

      The authentication protocol exchange consists of a series of
      server challenges and client responses that are specific to the
      authentication mechanism.  A server challenge consists of a
      command continuation request response with the "+" token followed
      by a BASE64 encoded string.  The client response consists of a
      single line consisting of a BASE64 encoded string.  If the client
      wishes to cancel an authentication exchange, it issues a line
      consisting of a single "*".  If the server receives such a
      response, it MUST reject the AUTHENTICATE command by sending a
      tagged BAD response.

      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 tagged OK response for the server.

      While client and server implementations MUST implement the
      AUTHENTICATE command itself, it is not required to implement any
      authentication mechanisms other than the PLAIN mechanism described

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      in [IMAP-TLS].  Also, an authentication mechanism is not required
      to support any security layers.

           Note: a server implementation MUST implement a
           configuration in which it does NOT permit any plaintext
           password mechanisms, unless either the STARTTLS command
           has been negotiated or some other mechanism that
           protects the session from password snooping has been
           provided.  Server sites SHOULD NOT use any configuration
           which permits a plaintext password mechanism without
           such a protection mechanism against password snooping.
           Client and server implementations SHOULD implement
           additional [SASL] mechanisms that do not use plaintext
           passwords, such the GSSAPI mechanism described in [SASL]
           and/or the [DIGEST-MD5] mechanism.

      Servers and clients can support multiple authentication
      mechanisms.  The server SHOULD list its supported authentication
      mechanisms in the response to the CAPABILITY command so that the
      client knows which authentication mechanisms to use.

      A server MAY include a CAPABILITY response code in the tagged OK
      response of a successful AUTHENTICATE command in order to send
      capabilities automatically.  It is unnecessary for a client to
      send a separate CAPABILITY command if it recognizes these
      automatic capabilities.  This should only be done if a security
      layer was not negotiated by the AUTHENTICATE command, because the
      tagged OK response as part of an AUTHENTICATE command is not
      protected by encryption/integrity checking.  [SASL] requires the
      client to re-issue a CAPABILITY command in this case.

      If an AUTHENTICATE command fails with a NO response, the client
      MAY try another authentication mechanism by issuing another
      AUTHENTICATE command.  It MAY also attempt to authenticate by
      using the LOGIN command (see section 6.2.3 for more detail).  In
      other words, the client MAY request authentication types in
      decreasing order of preference, with the LOGIN command as a last
      resort.

      The authorization identity passed from the client to the server
      during the authentication exchange is interpreted by the server as
      the user name whose privileges the client is requesting.

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   Example:    S: * OK IMAP4rev1 Server
               C: A001 AUTHENTICATE GSSAPI
               S: +
               C: YIIB+wYJKoZIhvcSAQICAQBuggHqMIIB5qADAgEFoQMCAQ6iBw
                  MFACAAAACjggEmYYIBIjCCAR6gAwIBBaESGxB1Lndhc2hpbmd0
                  b24uZWR1oi0wK6ADAgEDoSQwIhsEaW1hcBsac2hpdmFtcy5jYW
                  Mud2FzaGluZ3Rvbi5lZHWjgdMwgdCgAwIBAaEDAgEDooHDBIHA
                  cS1GSa5b+fXnPZNmXB9SjL8Ollj2SKyb+3S0iXMljen/jNkpJX
                  AleKTz6BQPzj8duz8EtoOuNfKgweViyn/9B9bccy1uuAE2HI0y
                  C/PHXNNU9ZrBziJ8Lm0tTNc98kUpjXnHZhsMcz5Mx2GR6dGknb
                  I0iaGcRerMUsWOuBmKKKRmVMMdR9T3EZdpqsBd7jZCNMWotjhi
                  vd5zovQlFqQ2Wjc2+y46vKP/iXxWIuQJuDiisyXF0Y8+5GTpAL
                  pHDc1/pIGmMIGjoAMCAQGigZsEgZg2on5mSuxoDHEA1w9bcW9n
                  FdFxDKpdrQhVGVRDIzcCMCTzvUboqb5KjY1NJKJsfjRQiBYBdE
                  NKfzK+g5DlV8nrw81uOcP8NOQCLR5XkoMHC0Dr/80ziQzbNqhx
                  O6652Npft0LQwJvenwDI13YxpwOdMXzkWZN/XrEqOWp6GCgXTB
                  vCyLWLlWnbaUkZdEYbKHBPjd8t/1x5Yg==
               S: + YGgGCSqGSIb3EgECAgIAb1kwV6ADAgEFoQMCAQ+iSzBJoAMC
                  AQGiQgRAtHTEuOP2BXb9sBYFR4SJlDZxmg39IxmRBOhXRKdDA0
                  uHTCOT9Bq3OsUTXUlk0CsFLoa8j+gvGDlgHuqzWHPSQg==
               C:
               S: + YDMGCSqGSIb3EgECAgIBAAD/////6jcyG4GE3KkTzBeBiVHe
                  ceP2CWY0SR0fAQAgAAQEBAQ=
               C: YDMGCSqGSIb3EgECAgIBAAD/////3LQBHXTpFfZgrejpLlLImP
                  wkhbfa2QteAQAgAG1yYwE=
               S: A001 OK GSSAPI authentication successful

        Note: The line breaks within server challenges and client
        responses are for editorial clarity and are not in real
        authenticators.


6.2.3.  LOGIN Command

   Arguments:  user name
               password

   Responses:  no specific responses for this command

   Result:     OK - login completed, now in authenticated state
               NO - login failure: user name or password rejected
               BAD - command unknown or arguments invalid

      The LOGIN command identifies the client to the server and carries
      the plaintext password authenticating this user.

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      A server MAY include a CAPABILITY response code in the tagged OK
      response to a successful LOGIN command in order to send
      capabilities automatically.  It is unnecessary for a client to
      send a separate CAPABILITY command if it recognizes these
      automatic capabilities.

   Example:    C: a001 LOGIN SMITH SESAME
               S: a001 OK LOGIN completed

        Note: Use of the LOGIN command over an insecure network
        (such as the Internet) is a security risk, because anyone
        monitoring network traffic can obtain plaintext passwords.
        The LOGIN command SHOULD NOT be used except as a last
        resort, and it is recommended that client implementations
        have a means to disable any automatic use of the LOGIN
        command.

        Unless either the STARTTLS command has been negotiated or
        some other mechanism that protects the session from
        password snooping has been provided, a server
        implementation MUST implement a configuration in which it
        advertises the LOGINDISABLED capability and does NOT permit
        the LOGIN command.  Server sites SHOULD NOT use any
        configuration which permits the LOGIN command without such
        a protection mechanism against password snooping.  A client
        implementation MUST NOT send a LOGIN command if the
        LOGINDISABLED capability is advertised.

6.3.    Client Commands - Authenticated State

   In the authenticated state, commands that manipulate mailboxes as
   atomic entities are permitted.  Of these commands, the SELECT and
   EXAMINE commands will select a mailbox for access and enter the
   selected state.

   In addition to the universal commands (CAPABILITY, NOOP, and LOGOUT),
   the following commands are valid in the authenticated state: SELECT,
   EXAMINE, CREATE, DELETE, RENAME, SUBSCRIBE, UNSUBSCRIBE, LIST, LSUB,
   STATUS, and APPEND.

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6.3.1.  SELECT Command

   Arguments:  mailbox name

   Responses:  REQUIRED untagged responses: FLAGS, EXISTS, RECENT
               REQUIRED OK untagged responses:  UNSEEN,  PERMANENTFLAGS,
               UIDNEXT, UIDVALIDITY

   Result:     OK - select completed, now in selected state
               NO - select failure, now in authenticated state: no
                    such mailbox, can't access mailbox
               BAD - command unknown or arguments invalid

      The SELECT command selects a mailbox so that messages in the
      mailbox can be accessed.  Before returning an OK to the client,
      the server MUST send the following untagged data to the client.
      Note that earlier versions of this protocol only required the
      FLAGS, EXISTS, and RECENT untagged data; consequently, client
      implementations SHOULD implement default behavior for missing data
      as discussed with the individual item.

         FLAGS       Defined flags in the mailbox.  See the description
                     of the FLAGS response for more detail.

         <n> EXISTS  The number of messages in the mailbox.  See the
                     description of the EXISTS response for more detail.

         <n> RECENT  The number of messages with the \Recent flag set.
                     See the description of the RECENT response for more
                     detail.

         OK [UNSEEN <n>]
                     The message sequence number of the first unseen
                     message in the mailbox.  If this is missing, the
                     client can not make any assumptions about the first
                     unseen message in the mailbox, and needs to issue a
                     SEARCH command if it wants to find it.

         OK [PERMANENTFLAGS (<list of flags>)]
                     A list of message flags that the client can change
                     permanently.  If this is missing, the client should
                     assume that all flags can be changed permanently.

         OK [UIDNEXT <n>]
                     The next unique identifier value.  Refer to section
                     2.3.1.1 for more information.  If this is missing,
                     the client can not make any assumptions about the
                     next unique identifier value.

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         OK [UIDVALIDITY <n>]
                     The unique identifier validity value.  Refer to
                     section 2.3.1.1 for more information.  If this is
                     missing, the server does not support unique
                     identifiers.

      Only one mailbox can be selected at a time in a connection;
      simultaneous access to multiple mailboxes requires multiple
      connections.  The SELECT command automatically deselects any
      currently selected mailbox before attempting the new selection.
      Consequently, if a mailbox is selected and a SELECT command that
      fails is attempted, no mailbox is selected.

      If the client is permitted to modify the mailbox, the server
      SHOULD prefix the text of the tagged OK response with the
      "[READ-WRITE]" response code.

      If the client is not permitted to modify the mailbox but is
      permitted read access, the mailbox is selected as read-only, and
      the server MUST prefix the text of the tagged OK response to
      SELECT with the "[READ-ONLY]" response code.  Read-only access
      through SELECT differs from the EXAMINE command in that certain
      read-only mailboxes MAY permit the change of permanent state on a
      per-user (as opposed to global) basis.  Netnews messages marked in
      a server-based .newsrc file are an example of such per-user
      permanent state that can be modified with read-only mailboxes.

   Example:    C: A142 SELECT INBOX
               S: * 172 EXISTS
               S: * 1 RECENT
               S: * OK [UNSEEN 12] Message 12 is first unseen
               S: * OK [UIDVALIDITY 3857529045] UIDs valid
               S: * OK [UIDNEXT 4392] Predicted next UID
               S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft)
               S: * OK [PERMANENTFLAGS (\Deleted \Seen \*)] Limited
               S: A142 OK [READ-WRITE] SELECT completed

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6.3.2.  EXAMINE Command

   Arguments:  mailbox name

   Responses:  REQUIRED untagged responses: FLAGS, EXISTS, RECENT
               REQUIRED OK untagged responses:  UNSEEN,  PERMANENTFLAGS,
               UIDNEXT, UIDVALIDITY

   Result:     OK - examine completed, now in selected state
               NO - examine failure, now in authenticated state: no
                    such mailbox, can't access mailbox
               BAD - command unknown or arguments invalid

      The EXAMINE command is identical to SELECT and returns the same
      output; however, the selected mailbox is identified as read-only.
      No changes to the permanent state of the mailbox, including
      per-user state, are permitted; in particular, EXAMINE MUST NOT
      cause messages to lose the \Recent flag.

      The text of the tagged OK response to the EXAMINE command MUST
      begin with the "[READ-ONLY]" response code.

   Example:    C: A932 EXAMINE blurdybloop
               S: * 17 EXISTS
               S: * 2 RECENT
               S: * OK [UNSEEN 8] Message 8 is first unseen
               S: * OK [UIDVALIDITY 3857529045] UIDs valid
               S: * OK [UIDNEXT 4392] Predicted next UID
               S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft)
               S: * OK [PERMANENTFLAGS ()] No permanent flags permitted
               S: A932 OK [READ-ONLY] EXAMINE completed


6.3.3.  CREATE Command

   Arguments:  mailbox name

   Responses:  no specific responses for this command

   Result:     OK - create completed
               NO - create failure: can't create mailbox with that name
               BAD - command unknown or arguments invalid

      The CREATE command creates a mailbox with the given name.  An OK
      response is returned only if a new mailbox with that name has been
      created.  It is an error to attempt to create INBOX or a mailbox
      with a name that refers to an extant mailbox.  Any error in
      creation will return a tagged NO response.

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      If the mailbox name is suffixed with the server's hierarchy
      separator character (as returned from the server by a LIST
      command), this is a declaration that the client intends to create
      mailbox names under this name in the hierarchy.  Server
      implementations that do not require this declaration MUST ignore
      the declaration.  In any case, the name created is without the
      trailing hierarchy delimiter.

      If the server's hierarchy separator character appears elsewhere in
      the name, the server SHOULD create any superior hierarchical names
      that are needed for the CREATE command to be successfully
      completed.  In other words, an attempt to create "foo/bar/zap" on
      a server in which "/" is the hierarchy separator character SHOULD
      create foo/ and foo/bar/ if they do not already exist.

      If a new mailbox is created with the same name as a mailbox which
      was deleted, its unique identifiers MUST be greater than any
      unique identifiers used in the previous incarnation of the mailbox
      UNLESS the new incarnation has a different unique identifier
      validity value.  See the description of the UID command for more
      detail.

   Example:    C: A003 CREATE owatagusiam/
               S: A003 OK CREATE completed
               C: A004 CREATE owatagusiam/blurdybloop
               S: A004 OK CREATE completed

        Note: The interpretation of this example depends on whether
        "/" was returned as the hierarchy separator from LIST.  If
        "/" is the hierarchy separator, a new level of hierarchy
        named "owatagusiam" with a member called "blurdybloop" is
        created.  Otherwise, two mailboxes at the same hierarchy
        level are created.


6.3.4.  DELETE Command

   Arguments:  mailbox name

   Responses:  no specific responses for this command

   Result:     OK - delete completed
               NO - delete failure: can't delete mailbox with that name
               BAD - command unknown or arguments invalid

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      The DELETE command permanently removes the mailbox with the given
      name.  A tagged OK response is returned only if the mailbox has
      been deleted.  It is an error to attempt to delete INBOX or a
      mailbox name that does not exist.

      The DELETE command MUST NOT remove inferior hierarchical names.
      For example, if a mailbox "foo" has an inferior "foo.bar"
      (assuming "." is the hierarchy delimiter character), removing
      "foo" MUST NOT remove "foo.bar".  It is an error to attempt to
      delete a name that has inferior hierarchical names and also has
      the \Noselect mailbox name attribute (see the description of the
      LIST response for more details).

      It is permitted to delete a name that has inferior hierarchical
      names and does not have the \Noselect mailbox name attribute.  In
      this case, all messages in that mailbox are removed, and the name
      will acquire the \Noselect mailbox name attribute.

      The value of the highest-used unique identifier of the deleted
      mailbox MUST be preserved so that a new mailbox created with the
      same name will not reuse the identifiers of the former
      incarnation, UNLESS the new incarnation has a different unique
      identifier validity value.  See the description of the UID command
      for more detail.

   Examples:   C: A682 LIST "" *
               S: * LIST () "/" blurdybloop
               S: * LIST (\Noselect) "/" foo
               S: * LIST () "/" foo/bar
               S: A682 OK LIST completed
               C: A683 DELETE blurdybloop
               S: A683 OK DELETE completed
               C: A684 DELETE foo
               S: A684 NO Name "foo" has inferior hierarchical names
               C: A685 DELETE foo/bar
               S: A685 OK DELETE Completed
               C: A686 LIST "" *
               S: * LIST (\Noselect) "/" foo
               S: A686 OK LIST completed
               C: A687 DELETE foo
               S: A687 OK DELETE Completed

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               C: A82 LIST "" *
               S: * LIST () "." blurdybloop
               S: * LIST () "." foo
               S: * LIST () "." foo.bar
               S: A82 OK LIST completed
               C: A83 DELETE blurdybloop
               S: A83 OK DELETE completed
               C: A84 DELETE foo
               S: A84 OK DELETE Completed
               C: A85 LIST "" *
               S: * LIST () "." foo.bar
               S: A85 OK LIST completed
               C: A86 LIST "" %
               S: * LIST (\Noselect) "." foo
               S: A86 OK LIST completed


6.3.5.  RENAME Command

   Arguments:  existing mailbox name
               new mailbox name

   Responses:  no specific responses for this command

   Result:     OK - rename completed
               NO - rename failure: can't rename mailbox with that name,
                    can't rename to mailbox with that name
               BAD - command unknown or arguments invalid

      The RENAME command changes the name of a mailbox.  A tagged OK
      response is returned only if the mailbox has been renamed.  It is
      an error to attempt to rename from a mailbox name that does not
      exist or to a mailbox name that already exists.  Any error in
      renaming will return a tagged NO response.

      If the name has inferior hierarchical names, then the inferior
      hierarchical names MUST also be renamed.  For example, a rename of
      "foo" to "zap" will rename "foo/bar" (assuming "/" is the
      hierarchy delimiter character) to "zap/bar".

      If the server's hierarchy separator character appears in the name,
      the server SHOULD create any superior hierarchical names that are
      needed for the RENAME command to complete successfully.  In other
      words, an attempt to rename "foo/bar/zap" to baz/rag/zowie on a
      server in which "/" is the hierarchy separator character SHOULD
      create baz/ and baz/rag/ if they do not already exist.

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      The value of the highest-used unique identifier of the old mailbox
      name MUST be preserved so that a new mailbox created with the same
      name will not reuse the identifiers of the former incarnation,
      UNLESS the new incarnation has a different unique identifier
      validity value.  See the description of the UID command for more
      detail.

      Renaming INBOX is permitted, and has special behavior.  It moves
      all messages in INBOX to a new mailbox with the given name,
      leaving INBOX empty.  If the server implementation supports
      inferior hierarchical names of INBOX, these are unaffected by a
      rename of INBOX.

   Examples:   C: A682 LIST "" *
               S: * LIST () "/" blurdybloop
               S: * LIST (\Noselect) "/" foo
               S: * LIST () "/" foo/bar
               S: A682 OK LIST completed
               C: A683 RENAME blurdybloop sarasoop
               S: A683 OK RENAME completed
               C: A684 RENAME foo zowie
               S: A684 OK RENAME Completed
               C: A685 LIST "" *
               S: * LIST () "/" sarasoop
               S: * LIST (\Noselect) "/" zowie
               S: * LIST () "/" zowie/bar
               S: A685 OK LIST completed

               C: Z432 LIST "" *
               S: * LIST () "." INBOX
               S: * LIST () "." INBOX.bar
               S: Z432 OK LIST completed
               C: Z433 RENAME INBOX old-mail
               S: Z433 OK RENAME completed
               C: Z434 LIST "" *
               S: * LIST () "." INBOX
               S: * LIST () "." INBOX.bar
               S: * LIST () "." old-mail
               S: Z434 OK LIST completed

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6.3.6.  SUBSCRIBE Command

   Arguments:  mailbox

   Responses:  no specific responses for this command

   Result:     OK - subscribe completed
               NO - subscribe failure: can't subscribe to that name
               BAD - command unknown or arguments invalid

      The SUBSCRIBE command adds the specified mailbox name to the
      server's set of "active" or "subscribed" mailboxes as returned by
      the LSUB command.  This command returns a tagged OK response only
      if the subscription is successful.

      A server MAY validate the mailbox argument to SUBSCRIBE to verify
      that it exists.  However, it MUST NOT unilaterally remove an
      existing mailbox name from the subscription list even if a mailbox
      by that name no longer exists.

           Note: This requirement is because a server site can
           choose to routinely remove a mailbox with a well-known
           name (e.g., "system-alerts") after its contents expire,
           with the intention of recreating it when new contents
           are appropriate.


   Example:    C: A002 SUBSCRIBE #news.comp.mail.mime
               S: A002 OK SUBSCRIBE completed


6.3.7.  UNSUBSCRIBE Command

   Arguments:  mailbox name

   Responses:  no specific responses for this command

   Result:     OK - unsubscribe completed
               NO - unsubscribe failure: can't unsubscribe that name
               BAD - command unknown or arguments invalid

      The UNSUBSCRIBE command removes the specified mailbox name from
      the server's set of "active" or "subscribed" mailboxes as returned
      by the LSUB command.  This command returns a tagged OK response
      only if the unsubscription is successful.

   Example:    C: A002 UNSUBSCRIBE #news.comp.mail.mime
               S: A002 OK UNSUBSCRIBE completed

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6.3.8.  LIST Command

   Arguments:  reference name
               mailbox name with possible wildcards

   Responses:  untagged responses: LIST

   Result:     OK - list completed
               NO - list failure: can't list that reference or name
               BAD - command unknown or arguments invalid

      The LIST command returns a subset of names from the complete set
      of all names available to the client.  Zero or more untagged LIST
      replies are returned, containing the name attributes, hierarchy
      delimiter, and name; see the description of the LIST reply for
      more detail.

      The LIST command SHOULD return its data quickly, without undue
      delay.  For example, it SHOULD NOT go to excess trouble to
      calculate the \Marked or \Unmarked status or perform other
      processing; if each name requires 1 second of processing, then a
      list of 1200 names would take 20 minutes!

      An empty ("" string) reference name argument indicates that the
      mailbox name is interpreted as by SELECT.  The returned mailbox
      names MUST match the supplied mailbox name pattern.  A non-empty
      reference name argument is the name of a mailbox or a level of
      mailbox hierarchy, and indicates the context in which the mailbox
      name is interpreted.

      An empty ("" string) mailbox name argument is a special request to
      return the hierarchy delimiter and the root name of the name given
      in the reference.  The value returned as the root MAY be the empty
      string if the reference is non-rooted or is an empty string.  In
      all cases, a hierarchy delimiter (or NIL if there is no hierarchy)
      is returned.  This permits a client to get the hierarchy delimiter
      (or find out that the mailbox names are flat) even when no
      mailboxes by that name currently exist.

      The reference and mailbox name arguments are interpreted into a
      canonical form that represents an unambiguous left-to-right
      hierarchy.  The returned mailbox names will be in the interpreted
      form.

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           Note: The interpretation of the reference argument is
           implementation-defined.  It depends upon whether the
           server implementation has a concept of the "current
           working directory" and leading "break out characters",
           which override the current working directory.

           For example, on a server which exports a UNIX or NT
           filesystem, the reference argument contains the current
           working directory, and the mailbox name argument would
           contain the name as interpreted in the current working
           directory.

           If a server implementation has no concept of break out
           characters, the canonical form is normally the reference
           name appended with the mailbox name.  Note that if the
           server implements the namespace convention (section
           5.1.2), "#" is a break out character and must be treated
           as such.

           If the reference argument is not a level of mailbox
           hierarchy (that is, it is a \NoInferiors name), and/or
           the reference argument does not end with the hierarchy
           delimiter, it is implementation-dependent how this is
           interpreted.  For example, a reference of "foo/bar" and
           mailbox name of "rag/baz" could be interpreted as
           "foo/bar/rag/baz", "foo/barrag/baz", or "foo/rag/baz".
           A client SHOULD NOT use such a reference argument except
           at the explicit request of the user.  A hierarchical
           browser MUST NOT make any assumptions about server
           interpretation of the reference unless the reference is
           a level of mailbox hierarchy AND ends with the hierarchy
           delimiter.

      Any part of the reference argument that is included in the
      interpreted form SHOULD prefix the interpreted form.  It SHOULD
      also be in the same form as the reference name argument.  This
      rule permits the client to determine if the returned mailbox name
      is in the context of the reference argument, or if something about
      the mailbox argument overrode the reference argument.  Without
      this rule, the client would have to have knowledge of the server's
      naming semantics including what characters are "breakouts" that
      override a naming context.

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           For example, here are some examples of how references
           and mailbox names might be interpreted on a UNIX-based
           server:

               Reference     Mailbox Name  Interpretation
               ------------  ------------  --------------
               ~smith/Mail/  foo.*         ~smith/Mail/foo.*
               archive/      %             archive/%
               #news.        comp.mail.*   #news.comp.mail.*
               ~smith/Mail/  /usr/doc/foo  /usr/doc/foo
               archive/      ~fred/Mail/*  ~fred/Mail/*

           The first three examples demonstrate interpretations in
           the context of the reference argument.  Note that
           "~smith/Mail" SHOULD NOT be transformed into something
           like "/u2/users/smith/Mail", or it would be impossible
           for the client to determine that the interpretation was
           in the context of the reference.

      The character "*" is a wildcard, and matches zero or more
      characters at this position.  The character "%" is similar to "*",
      but it does not match a hierarchy delimiter.  If the "%" wildcard
      is the last character of a mailbox name argument, matching levels
      of hierarchy are also returned.  If these levels of hierarchy are
      not also selectable mailboxes, they are returned with the
      \Noselect mailbox name attribute (see the description of the LIST
      response for more details).

      Server implementations are permitted to "hide" otherwise
      accessible mailboxes from the wildcard characters, by preventing
      certain characters or names from matching a wildcard in certain
      situations.  For example, a UNIX-based server might restrict the
      interpretation of "*" so that an initial "/" character does not
      match.

      The special name INBOX is included in the output from LIST, if
      INBOX is supported by this server for this user and if the
      uppercase string "INBOX" matches the interpreted reference and
      mailbox name arguments with wildcards as described above.  The
      criteria for omitting INBOX is whether SELECT INBOX will return
      failure; it is not relevant whether the user's real INBOX resides
      on this or some other server.

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   Example:    C: A101 LIST "" ""
               S: * LIST (\Noselect) "/" ""
               S: A101 OK LIST Completed
               C: A102 LIST #news.comp.mail.misc ""
               S: * LIST (\Noselect) "." #news.
               S: A102 OK LIST Completed
               C: A103 LIST /usr/staff/jones ""
               S: * LIST (\Noselect) "/" /
               S: A103 OK LIST Completed
               C: A202 LIST ~/Mail/ %
               S: * LIST (\Noselect) "/" ~/Mail/foo
               S: * LIST () "/" ~/Mail/meetings
               S: A202 OK LIST completed


6.3.9.  LSUB Command

   Arguments:  reference name
               mailbox name with possible wildcards

   Responses:  untagged responses: LSUB

   Result:     OK - lsub completed
               NO - lsub failure: can't list that reference or name
               BAD - command unknown or arguments invalid

      The LSUB command returns a subset of names from the set of names
      that the user has declared as being "active" or "subscribed".
      Zero or more untagged LSUB replies are returned.  The arguments to
      LSUB are in the same form as those for LIST.

      The returned untagged LSUB response MAY contain different mailbox
      flags from a LIST untagged response.  If this should happen, the
      flags in the untagged LIST are considered more authoritative.

      A special situation occurs when using LSUB with the % wildcard.
      Consider what happens if "foo/bar" (with a hierarchy delimiter of
      "/") is subscribed but "foo" is not.  A "%" wildcard to LSUB must
      return foo, not foo/bar, in the LSUB response, and it MUST be
      flagged with the \Noselect attribute.

      The server MUST NOT unilaterally remove an existing mailbox name
      from the subscription list even if a mailbox by that name no
      longer exists.

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   Example:    C: A002 LSUB "#news." "comp.mail.*"
               S: * LSUB () "." #news.comp.mail.mime
               S: * LSUB () "." #news.comp.mail.misc
               S: A002 OK LSUB completed
               C: A003 LSUB "#news." "comp.%"
               S: * LSUB (\NoSelect) "." #news.comp.mail
               S: A003 OK LSUB completed


6.3.10. STATUS Command

   Arguments:  mailbox name
               status data item names

   Responses:  untagged responses: STATUS

   Result:     OK - status completed
               NO - status failure: no status for that name
               BAD - command unknown or arguments invalid

      The STATUS command requests the status of the indicated mailbox.
      It does not change the currently selected mailbox, nor does it
      affect the state of any messages in the queried mailbox (in
      particular, STATUS MUST NOT cause messages to lose the \Recent
      flag).

      The STATUS command provides an alternative to opening a second
      IMAP4rev1 connection and doing an EXAMINE command on a mailbox to
      query that mailbox's status without deselecting the current
      mailbox in the first IMAP4rev1 connection.

      Unlike the LIST command, the STATUS command is not guaranteed to
      be fast in its response.  Under certain circumstances, it can be
      quite slow.  In some implementations, the server is obliged to
      open the mailbox read-only internally to obtain certain status
      information.  Also unlike the LIST command, the STATUS command
      does not accept wildcards.

           Note: The STATUS command is intended to access the
           status of mailboxes other than the currently selected
           mailbox.  Because the STATUS command can cause the
           mailbox to be opened internally, and because this
           information is available by other means on the selected
           mailbox, the STATUS command SHOULD NOT be used on the
           currently selected mailbox.

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           The STATUS command MUST NOT be used as a "check for new
           messages in the selected mailbox" operation (refer to
           sections 7, 7.3.1, and 7.3.2 for more information about
           the proper method for new message checking).

           Because the STATUS command is not guaranteed to be fast
           in its results, clients SHOULD NOT expect to be able to
           issue many consecutive STATUS commands and obtain
           reasonable performance.

      The currently defined status data items that can be requested are:

      MESSAGES
         The number of messages in the mailbox.

      RECENT
         The number of messages with the \Recent flag set.

      UIDNEXT
         The next unique identifier value of the mailbox.  Refer to
         section 2.3.1.1 for more information.

      UIDVALIDITY
         The unique identifier validity value of the mailbox.  Refer to
         section 2.3.1.1 for more information.

      UNSEEN
         The number of messages which do not have the \Seen flag set.


   Example:    C: A042 STATUS blurdybloop (UIDNEXT MESSAGES)
               S: * STATUS blurdybloop (MESSAGES 231 UIDNEXT 44292)
               S: A042 OK STATUS completed

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6.3.11. APPEND Command

   Arguments:  mailbox name
               OPTIONAL flag parenthesized list
               OPTIONAL date/time string
               message literal

   Responses:  no specific responses for this command

   Result:     OK - append completed
               NO - append error: can't append to that mailbox, error
                    in flags or date/time or message text
               BAD - command unknown or arguments invalid

      The APPEND command appends the literal argument as a new message
      to the end of the specified destination mailbox.  This argument
      SHOULD be in the format of an [RFC-2822] message.  8-bit
      characters are permitted in the message.  A server implementation
      that is unable to preserve 8-bit data properly MUST be able to
      reversibly convert 8-bit APPEND data to 7-bit using a [MIME-IMB]
      content transfer encoding.

           Note: There MAY be exceptions, e.g., draft messages, in
           which required [RFC-2822] header lines are omitted in
           the message literal argument to APPEND.  The full
           implications of doing so MUST be understood and
           carefully weighed.

      If a flag parenthesized list is specified, the flags SHOULD be set
      in the resulting message; otherwise, the flag list of the
      resulting message is set to empty by default.  In either case, the
      Recent flag is also set.

      If a date-time is specified, the internal date SHOULD be set in
      the resulting message; otherwise, the internal date of the
      resulting message is set to the current date and time by default.

      If the append is unsuccessful for any reason, the mailbox MUST be
      restored to its state before the APPEND attempt; no partial
      appending is permitted.

      If the destination mailbox does not exist, a server MUST return an
      error, and MUST NOT automatically create the mailbox.  Unless it
      is certain that the destination mailbox can not be created, the
      server MUST send the response code "[TRYCREATE]" as the prefix of
      the text of the tagged NO response.  This gives a hint to the
      client that it can attempt a CREATE command and retry the APPEND
      if the CREATE is successful.

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      If the mailbox is currently selected, the normal new message
      actions SHOULD occur.  Specifically, the server SHOULD notify the
      client immediately via an untagged EXISTS response.  If the server
      does not do so, the client MAY issue a NOOP command (or failing
      that, a CHECK command) after one or more APPEND commands.

   Example:    C: A003 APPEND saved-messages (\Seen) {310}
               S: + Ready for literal data
               C: Date: Mon, 7 Feb 1994 21:52:25 -0800 (PST)
               C: From: Fred Foobar <foobar@Blurdybloop.COM>
               C: Subject: afternoon meeting
               C: To: mooch@owatagu.siam.edu
               C: Message-Id: <B27397-0100000@Blurdybloop.COM>
               C: MIME-Version: 1.0
               C: Content-Type: TEXT/PLAIN; CHARSET=US-ASCII
               C:
               C: Hello Joe, do you think we can meet at 3:30 tomorrow?
               C:
               S: A003 OK APPEND completed

        Note: The APPEND command is not used for message delivery,
        because it does not provide a mechanism to transfer [SMTP]
        envelope information.



(page 47 continued on part 3)

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