RFC 1730 (rfc1730) - Page 2 of 73

Internet Message Access Protocol - Version 4

RFC 1730                         IMAP4                     December 1994


2.2.1.  Client Protocol Sender and Server Protocol Receiver

   The client command begins an operation.  Each client command is
   prefixed with a identifier (typically a short alphanumeric string,
   e.g. A0001, A0002, etc.) called a "tag".  A different tag is
   generated by the client for each command.

   There are two cases in which a line from the client does not
   represent a complete command.  In one case, a command argument is
   quoted with an octet count (see the description of literal in String
   under Data Formats); in the other case, the command arguments require
   server feedback (see the AUTHENTICATE command).  In either case, the
   server sends a command continuation request response if it is ready
   for the octets (if appropriate) and the remainder of the command.
   This response is prefixed with the token "+".

        Note: If, instead, the server detected an error in the
        command, it sends a BAD completion response with tag
        matching the command (as described below) to reject the
        command and prevent the client from sending any more of the
        command.

        It is also possible for the server to send a completion
        response for some other command (if multiple commands are
        in progress), or untagged data.  In either case, the
        command continuation request is still pending; the client
        takes the appropriate action for the response, and reads
        another response from the server.

   The protocol receiver of an IMAP4 server reads a command line from
   the client, parses the command and its arguments, and transmits
   server data and a server command completion result response.


2.2.2.  Server Protocol Sender and Client Protocol Receiver

   Data transmitted by the server to the client and status responses
   that do not indicate command completion are prefixed with the token
   "*", and are called untagged responses.

   Server data may be sent as a result of a client command, or may be
   sent unilaterally by the server.  There is no syntactic difference
   between server data that resulted from a specific command and server
   data that were sent unilaterally.

   The server completion result response indicates the success or
   failure of the operation.  It is tagged with the same tag as the
   client command which began the operation.  Thus, if more than one



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