IMAP is the email retrieval protocol that lets clients manage messages on a mail server.
IMAP stands for Internet Message Access Protocol. Unlike a basic download-oriented workflow, IMAP is designed for remote mailbox management: clients can read, flag, organize, search, move, and delete messages while the mailbox remains on the server. This makes the same folders and message state available across phones, computers, and webmail interfaces.
IMAP was developed in the 1980s by Mark Crispin as a remote-access alternative to POP. Its server-centered model supports multiple clients and features such as folders, message flags, server-side searches, and the IMAP IDLE extension, which can notify a client about mailbox changes. IMAP usually uses TCP port 143, while IMAP over SSL/TLS commonly uses port 993.
POP3 can retrieve mail, but it is primarily download-oriented and offers less shared mailbox state. SMTP is used mainly for sending outgoing mail, not for managing an inbox.