Short for Internet Message Access Protocol, IMAP was first developed by Mark Crispin while at Stanford University in 1986. It is a protocol for retrieving e-mail from a server, similar to POP. The secure version of IMAP is called IMAPS, which stands for IMAP over SSL.
IMAP4 is the latest version of IMAP. It is similar to POP3, but with additional features.
IMAP defaults to port 143. IMAP4 uses port 993 over TLS/SSL.