Internet Message Access Protocol (IMAP) is a method of accessing electronic mail or bulletin board messages that are kept on a mail server. IMAP permits a "client" email program to access remote message stores as if they were local. Email stored on an IMAP server can be manipulated from a desktop computer remotely, without the need to transfer messages or files back and forth between these computers.

There are several different technologies and approaches to building a distributed electronic mail infrastructure. Among them: POP (Post Office Protocol), DMSP (Distributed Mail System Protocol), and IMAP (Internet Message Access Protocol). Of the three, POP is the oldest and consequently the best known. DMSP is largely limited to a single application, PCMAIL, and is known primarily for its excellent support of "disconnected" operation. IMAP offers a superset of POP and DMSP capabilities, and provides good support for all three modes of remote mailbox access: offline, online, and disconnected.

In the online mode, the mail client does not copy mails in a shared server all at once and then delete them. It is an interactive client-server model, where the client can ask the server for headers, or the bodies of specified messages, or to search for messages meeting certain criteria. Messages in the mail repository can be marked with various status flags (e.g. "deleted" or "answered") and they stay in the repository until explicitly removed by the user. IMAP is designed to permit manipulation of remote mailboxes as if they were local. Depending on the IMAP client implementation and the mail architecture desired by the system manager, the user may save messages directly on the client machine, or save them on the server, or be given the choice of doing either.

IMAP includes operations for creating, deleting, and renaming mailboxes; checking for new messages; permanently removing messages; setting and clearing flags; server-based and MIME parsing, and searching; and selective fetching of message attributes, texts, and portions thereof for efficiency. IMAP allows clients to access messages (both new and saved) from more than one computer, that feature has become extremely important as reliance on electronic messaging and use of multiple computers increase.

The current version of IMAP is version 4 revision 1(IMAP4 rev1). Key features for IMAP4 include:

• Fully compatible with Internet messaging standards, e.g. MIME.
• Allow message access and management from more than one computer.
• Allow access without reliance on less efficient file access protocols.
• Provide support for "online", "offline", and "disconnected" access modes *
• Support for concurrent access to shared mailboxes
• Client software needs no knowledge about the server"s file store format.

Protocol Structure

IMAP4 key commands:

Related Terms: SMTP, POP, POP3, TCP, MIME

Sponsor Source: IMAP is defined by IETF (http://www.ietf.org).

Reference:
http://www.javvin.com/protocol/rfc3501.pdf: INTERNET MESSAGE ACCESS PROTOCOL - VERSION 4rev1