Internet Message Access Protocol (IMAP) is an email protocol that allows users to access incoming email messages from an email server through an email client (email service provider) such as Outlook, Gmail, etc. IMAP works on the same lines as Post Office Protocol (POP) but unlike POP it doesn’t delete the email message from the mail server once the email is downloaded. IMAP keeps the original message on the server and lets users download only a copy. This means the message can also be viewed on another device connected to the server.

With most people owning multiple computing devices such as laptops, tablet computers, and smartphones, this synchronization between devices or the ability to contact an email server from different devices is invaluable. And this is a major reason why IMAP is preferred over POP in multi-device scenarios. IMAP enables accessing email messages from any device and location. The synchronization also means messages sent or responses to a particular message from a device also get registered on another device. That said, if an email message is deleted on a particular device, it would no longer be accessible from any of the connected devices.

IMAP History and Versions

IMAP came into being in 1986. It was developed at Stanford University by Mark Crispin. The protocol was later revised and released as IMAP2 in 1988. IMAP2 was formally documented in Request for Comments (RFC) 1064. IMAP2 was later updated in August 1990 in RFC 1176. By the way, RFC is a formal publication by the Internet Engineering Task Force (IETF) defining Internet standards.

A counter version to RFC 1176 was created in February 1991 in RFC 1203. IMAP3 wasn’t as widely used as IMAP2. In fact, IMAP2 was more widespread even after IMAP3 happened. An IMAP2 extension was also created, called IMAP2bis. It was released to add Multi-Purpose Internet Mail Extensions (MIME) support to IMAP. MIME lets people exchange various data files online such as video, audio, images, application, etc. But IMAP2bis was not recognized as an Internet standard, or it didn’t become an RFC.

IMAP4 was released in December 1994. It was published in RFC 1730 and RFC 1731. RFC 1730 described the protocol, and RFC 1731 threw light on IMAP4’s authentication mechanisms. IMAP4 has had seen quite a few refinements over the years, but nothing major to be called IMAP5. IMAP4 was first refined in 1996, allowing both plain and encrypted text login passwords.

IMAP Ports

IMAP protocol’s default port is port 143. Port 143 and port 993 are encrypted versions. Most desktop mail clients and webmail services such as Gmail, Outlook, Yahoo Mail, AOL, etc. use port 993.