The Internet Message Access Protocol (commonly known as IMAP) is an Internet protocol that allows an email client to access email on a remote mail server. An IMAP server typically listens on port 143. IMAP over SSL is assigned port number 993.
IMAP supports both on-line and off-line modes of operation. 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 while maintaining "sync" regardless of which client, device or application is used to view, send or receive email.
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. Most clients support the Internet standard protocols, SMTP for sending e-mail and POP and IMAP for retrieving email, allowing interoperability with other servers and clients.