IMAP and POP3 are the two most commonly used Internet mail protocols for retrieving emails. POP3 and IMAP are 2 different methods used to access mail from a third-party email client or software. he IMAP server listens on port 143, and the IMAP with SSL secure(IMAPDS) server listens on port 993. In fact, there is a major difference between the two protocols. Both POP3 and IMAP are protocols used between mail clients and email servers to access messages.