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The TCP/IP Guide

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Table Of Contents  The TCP/IP Guide
 9  TCP/IP Application Layer Protocols, Services and Applications (OSI Layers 5, 6 and 7)
      9  TCP/IP Key Applications and Application Protocols
           9  TCP/IP File and Message Transfer Applications and Protocols (FTP, TFTP, Electronic Mail, USENET, HTTP/WWW, Gopher)
                9  TCP/IP Electronic Mail System: Concepts and Protocols (RFC 822, MIME, SMTP, POP3, IMAP)
                     9  TCP/IP Electronic Mail Access and Retrieval Protocols and Methods
                          9  TCP/IP Internet Message Access Protocol (IMAP/IMAP4)

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IMAP General Operation, Client/Server Communication and Session States
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IMAP Not Authenticated State: User Authentication Process and Commands
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IMAP Commands, Results and Responses
(Page 4 of 4)

Result Codes

There are three main result codes sent in reply to a command, and two special ones used in certain circumstances:

  • OK: A positive result to a command, usually sent with the tag of the command that was successful. May be sent untagged in the server's initial greeting when a session starts.

  • NO: A negative result to a command. When tagged, indicates the command failed; when untagged, serves as a general warning message about some situation on the server.

  • BAD: Indicates an error message. It is tagged when the error is directly related to a command that has been sent, and otherwise is untagged.

  • PREAUTH: An untagged message sent at the start of a session to indicate that no authentication is required; the session goes directly to the Authenticated state.

  • BYE: Sent when the server is about to close the connection. It is always untagged, and is sent in reply to a Logout command or when the connection is to be closed for any other reason.
Response Codes

In contrast to results, responses are used to communicate a wide variety of information to the client device. Responses normally include descriptive text that provides details about what is being communicated. They may be sent either directly in reply to a command or incidentally to one. An example of the latter case would be if a new message arrives in a mailbox during a session. In this case, the server will convey this information “unilaterally” at its first opportunity, regardless of what command was recently sent.

The following are the response codes defined by the IMAP standard:

  • ALERT: An alert message to be sent to the human user of the IMAP client to inform him or her of something important.

  • BADCHARSET: Sent when a search fails due to use of an unsupported character set.

  • CAPABILITY: A list of server capabilities; may be sent as part of the initial server greeting so the CAPABILITY command does not need to be used.

  • PARSE: Sent when an error occurs parsing the headers or MIME content of an e-mail message.

  • PERMANENTFLAGS: Communicates a list of message status flags that the client is allowed to manipulate.

  • READ-ONLY: Tells the client that the mailbox is only accessible in a read-only mode.

  • READ-WRITE: Tells the client that the mailbox is accessible in read-write mode.

  • TRYCREATE: Sent when an APPEND or COPY command fails due to the target mailbox not existing, to suggest to the client that it try creating the mailbox first.

  • UIDNEXT: Sent with a decimal number that specifies the next unique identifier value to use in an operation. These identifiers allow each message to be uniquely identified.

  • UIDVALIDITY: Sent with a decimal number that specifies the unique identifier validity value, used to confirm unique message identification.

  • UNSEEN: Sent with a decimal number that tells the client the message that is flagged as not yet seen (a new message).

Previous Topic/Section
IMAP General Operation, Client/Server Communication and Session States
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Next Page
IMAP Not Authenticated State: User Authentication Process and Commands
Next Topic/Section

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Version 3.0 - Version Date: September 20, 2005

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