IMAP is an email retrieval protocol that allows multiple clients to manage a mailbox simultaneously. It has advantages over POP, including the ability to upload parts of an email and store mailbox and message status changes on the server. IMAP also supports custom keyword tags and efficient searching. It encrypts user and password information during login and supports extensions for mobile devices.
Internet Message Access Protocol is one of the two most common email retrieval protocols. Also known by the acronym IMAP, it is an Internet protocol that operates at the application layer. With IMAP, a mailbox can be read and managed simultaneously by several email clients. IMAP is often used by a large percentage of Internet users to download email from web mail servers.
Originally called the Interim Mail Access Protocol, the first version of IMAP has gone through several revisions since it was created in 1986. Version 2 was published in 1988 as Request For Comments (RFC) 1064 by the Internet Engineering Task Force (IETF). It changed the acronym IMAP to Interactive Mail Access Protocol and was revised again in 1990 by RFC 1176. An enhancement of version 2 that supports Multipurpose Internet Mail Extensions (MIME) is the basis for version 4. Although it was proposed in 1993, IMAP version 3 was never adopted and was scrapped in favor of version 4.
Now called the Internet Message Access Protocol, version 4 became the standard in 1994, published in RFC 1730. Design flaws caused it to be replaced in 1996 by IMAP version 4 revision 1, which was further refined in 2003 by RFC 3501 All previous versions and revisions are effectively obsolete and unused.
Post Office Protocol (POP) is the other common Internet protocol for retrieving email. Most email servers and clients support POP and Internet Message Access Protocol as well as their own unique protocols. Compared to POP, IMAP has many advantages including the ability to upload part of an email instead of waiting for all the attachments. It can also transmit message content using the MIME mechanism. IMAP clients also tend to stay connected to a mail server for longer periods, which can improve overall response times.
Mailbox and message status changes made by other clients connected at the same time are stored on the mail server by IMAP. Since POP doesn’t do this, it has no way to determine if another client has already read a message, for example. Some Internet Message Access Protocol servers also support custom keyword tags attached to e-mail messages. IMAP also provides an efficient server-based system for searching a mailbox for specific content without downloading all messages.
Server mailbox and message handling functions are included in IMAP, allowing clients to easily edit mailboxes. Extensions to core Internet Message Access Protocol features are also supported. One of the most common extensions creates an efficient means for mobile devices to store copies of sent emails. IMAP also encrypts user and password information during login, rather than exposing it in plain text like some other protocols.
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