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(Internet Message Access Protocol 4) A programming interface (API) from the IETF that enables a user's e-mail program to access the mail server (RFC 3501 standard). E-mail clients such as Outlook, Mail, Eudora and Thunderbird are typically configured to retrieve mail either via IMAP4 or POP3, the other popular standard.

IMAP4 has more options than POP3. For example, it can download only the message headers, which have only to/from addresses and subject. An essential option in the early days of dial-up, the user then chooses which messages and attachments to download. IMAP also keeps the messages on the mail server in synchronization with the downloaded messages in the client. Users can then decide when and which messages to delete on the server.

IMAP Flexibility for Web Mail
Although mail services provide a Web browser interface for managing mail, users often prefer to get mail via their favorite e-mail client, configured for IMAP4 or POP3. In addition, some users like to keep their e-mail online indefinitely for future searching. In such cases, IMAP4 offers the flexibility of selectively retaining messages, whereas POP3 does not. See POP3, e-mail interfaces, SMTP and messaging system.

Incoming Mail Options
Most Internet mail services offer all three options. IMAP4 provides the most flexibility. Users can store their messages locally and have it synchronized with the server. In addition, IMAP4 lets multiple users access the same mailbox simultaneously.
References in periodicals archive ?
IMAP4 -- Rapidly becoming the preferred industry standard for Internet
New Mail Manager utility -- With the implementation of IMAP4, careful
1 represents our second generation of IMAP4 client technology," said Bob Lawton, vice president of Emerging Technology Marketing for NetManage.
One of the areas in which SMTP/MIME-based messaging systems with an IMAP4 message store provided significant cost advantages was in administrative support required per user.
Key findings showed that SMTP/MIME with IMAP4 systems, when compared to Lotus Notes Release 4 and Microsoft Exchange:
Eighteen months ago there were hardly any IMAP4 servers; now there are more than 20.
Control Data's IntraStore Server is one IMAP4 server on the market today.
IMAP4 is a key addition for current ZMail users who will benefit from the flexible host-based mail features that IMAP4 provides.
The solution integrates with Microsoft Exchange, Lotus Domino and other groupware environments via POP3 or IMAP4.
Two major Fortune 500 corporations recently licensed the Shuttle to migrate thousands of user e-mail accounts within their corporations from TAO to Microsoft(R) Exchange and GroupWise(R) Notes(R) to an IMAP4 system.
Out-of-the-box personal and corporate e-mail solutions, including POP3, IMAP4, and Microsoft ActiveSync for wireless synchronization to Microsoft Exchange 2003,