In computing, the Internet Message Access Protocol (IMAP) is an Internet standard protocol used by email clients to retrieve email messages from a mail server over a TCP/IP connection. IMAP is defined by RFC 3501.
IMAP was designed with the goal of permitting complete management of an email box by multiple email clients, therefore clients generally leave messages on the server until the user explicitly deletes them. An IMAP server typically listens on port number 143. IMAP over SSL/TLS (IMAPS) is assigned the port number 993.
Virtually all modern e-mail clients and servers support IMAP, which along with the earlier POP3 (Post Office Protocol) are the two most prevalent standard protocols for email retrieval. Many webmail service providers such as Gmail and Outlook.com also provide support for both IMAP and POP3.
The Internet Message Access Protocol is an Application Layer Internet protocol that allows an e-mail client to access email on a remote mail server. The current version is defined by RFC 3501. An IMAP server typically listens on well-known port 143, while IMAP over SSL/TLS (IMAPS) uses 993.
Incoming email messages are sent to an email server that stores messages in the recipient's email box. The user retrieves the messages with an email client that uses one of a number of email retrieval protocols. While some clients and servers preferentially use vendor-specific, proprietary protocols, almost all support POP and IMAP for retrieving email – allowing many free choice between many e-mail clients such as Pegasus Mail or Mozilla Thunderbirdto access these servers, and allows the clients to be used with other servers.
Email clients using IMAP generally leave messages on the server until the user explicitly deletes them. This and other characteristics of IMAP operation allow multiple clients to manage the same mailbox. Most email clients support IMAP in addition to Post Office Protocol (POP) to retrieve messages. IMAP offers access to the mail storage. Clients may store local copies of the messages, but these are considered to be a temporary cache.
