IMAP (en)

In computing, the Internet Message Access Protocol (IMAP) is a standard Internet protocol used by email clients to retrieve email messages from a mail server via a TCP/IP connection. IMAP is defined by RFC 3501.

IMAP is designed to allow comprehensive management of an email inbox with multiple email clients, thus clients generally leave messages on the server until the user explicitly deletes them. IMAP servers usually listen on port number 143. IMAP over SSL (IMAPS) uses port number 993.

Almost all modern email clients and servers support IMAP. IMAP and the earlier POP3 (Post Office Protocol) are the two most commonly used protocols for retrieving email, with many webmail providers such as Gmail, Outlook.com, and Yahoo! Mail also offering support for both IMAP and POP3.