(Internet Message Access Protocol) A standard interface between an e-mail client program and the mail server, as defined by IETF RFC 3501. IMAP4 and POP3 are the two common access protocols used for Internet e-mail. IMAP4 provides a message store that holds incoming e-mail until users log in and download it.

Whereas POP3 downloads the entire message with attachments when mail is checked, IMAP4 can be configured to download only the headers, which display to/from addresses and subject. The user can then selectively download messages and attachments. See POP3, SMTP and messaging system.