RFC 1730 (rfc1730) - Page 2 of 73
Internet Message Access Protocol - Version 4
Alternative Format: Original Text Document
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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