IMAP

If you are a perpetual user of the internet and its services such as email, then the chances are high that you've come across the term, IMAP or Internet Message Access Protocol. IMAP, in layman's term, is a technique of retrieving e-mails from a mail server using a suitable e-mail client.

Normally, you don't see people using this method on a day to day level and that's because of another protocol, POP3 or Post Office Protocol, which is quite popular among the users. As of today, almost every e-mail client and server supports both of the protocols. The prime example of the e-mail client and server would be Mozilla Thunderbird and Gmail, respectively.

Before going to the history of IMAP, let's understand the basics of it. An E-mail client works in two modes, online and offline, and IMAP supports both of them. It is a protocol which operates on port 143 and thus allows the client to access the e-mails on a remote server. The client using IMAP downloads the e-mail from the server but doesn't delete it. This in turn, allows multiple clients to access the mailbox which is not possible in the case of POP3 as it was designed to work best on a single computer.

IMAP includes operations for the following -

1. Checking new messages.
2. Permanently deleting messages from the server.
3. Creating and deleting mailboxes.
4. Setting and clearing flags.
5. Fetching of message attributes.

IMAP is the brainchild of Mark Crispin, who designed it as a remote mailbox protocol, at Stanford University in 1986. The original version of IMAP, Interim Mail Access Protocol, was implemented as a Xerox Lisp machine client and a TOPS-20 server. But, it was quickly replaced by IMAP2 (Interactive Mail Access Protocol), as it introduced command/response tagging.

Later, it was extended to support MIME, Multipurpose Internet Mail Extensions, and its body structures and add mailbox management functionality which were absent in IMAP2. This new version was called IMAP2bis.

In the early 1990s, an IMAP Working Group was formed in the IETF which took over the job for the IMAP2bis design. In order to steer clear of the confusion with an IMAP3 proposal, they decided to rename it to IMAP4. Just two years later, it was replaced by IMAP4rev1, due to the faults that were found during the implementation experience. As a repercussion of this, there were very few clients which supported IMAP4.

The contemporary version of IMAP since 1996 is IMAP4rev1 or IMAP version 4 revision 1. It is said to be upward compatible with all the previous versions; IMAP2, IMAP2bis and IMAP4. It supports encrypted login mechanisms but Plain-text transmission of passwords is also possible. IMAP4 traffic can also be encrypted using SSL.

IMAP is known to have number of advantages over POP3 and few of them are

1. IMAP4 clients can create, delete, and rename mailboxes on the server, and move messages between mailboxes.
2. IMAP4 protocol allows simultaneous access to multiple e-mail clients and provides mediums for clients to detect changes made to the mailbox by other clients whereas POP3 protocol requires only one client to be connected to the mailbox at any given time.
3. While POP3 clients connect to the server for a short period of time, IMAP4, on the other hand, stay connected as long as the user interface is active.

Some key goals of IMAP4 are:

1. Bestow support for both online and offline mode.
2. Become fully compatible with Internet messaging standards, for example; MIME, as discussed earlier.
3. Provide message access from more than one computer.

Following are the common IMAP clients -

1. Apple Mail
2. iPhone's mail client
3. Eudora (e-mail client)
4. Microsoft Outlook Express
5. Windows Mail
6. Mozilla Thunderbird
7. The Bat!