Doc Searls wrote : "When I stupidly started downloading a grand or more of emails from the airport on the way to a plane in Miami yesterday, and even more stupidly tried to hasten the process in the midst, the laptop crashed, scrambling directories of approximately 10,000 messages. Some, I suspect, were lost."

When I read the complaint of Doc on his Email problems, I thought to myself: "why doesn't he use IMAP?" and then I thought "almost nobody does" so I decided to write this page for Doc and others.

What is IMAP?

IMAP (Internet Message Access Protocol) is a protocol for accessing Email on a remote server. Its predecessor (and more popular) protocol, POP (Post Office Protocol) is an "offline protocol". When using POP3, the mail client downloads all the mail that in the mailbox and then the user can read the mail. IMAP is an "online protocol". Talking IMAP to the server, the mail client downloads from the server the description of the messages based upon their headeres and MIME structure. When the user wants to read a certain message, the mail client downloads the body and attachements of this message only.


What are the benefits of using IMAP?

Speed (1). With IMAP, you download only the headers of the messages. You read only what you want.

Spam control. Using IMAP, the user (or a mail client using mail rules) can filter spam without the need to waste downloading time and effort. A user can read subject lines and sender names and then decides if he wants to read the message or delete it.

Private Folders. The IMAP protocol enables the user to manage her mail by creating folders on the server and move messages to those folders.

Public Folders. Certain servers (MS Exchange for example) can have public folders that users can create and subscribe to.

Speed (2). There are companies that use Microsoft Exchange and have people who travel a lot or work from home. Companies that are not aware of the IMAP capabilities of MS Exchange teach their employees to access their mail using Outlook/RPC (very slow) or POP3 (faster but still slow). MS Exchange has IMAP capabilities "out of the box" so no software should be installed or setup. Using IMAP, employees can access their mail AND the public folders on the server, which is a productivity plus.

What mail software supports IMAP?

Surprise surprise! Almost all popular ones. Microsoft Outlook and Outlook Express, Netscape mail clients, Pocomail, Pine. More can be found here.

I am convinced. Does my ISP support IMAP?

Call and ask.

The reason IMAP is often called "the best-kept secret in electronic messaging" is that ISP's don't encourage its use. IMAP enables storing Email messages on the server so the ISP should have more space for the mail of his clients. Also, the clients will expect some sort of backup for their important information. With POP3, the ISP only stores the messaged until they are downloaded (unless the user specifies "leave on server" which is NOT the default).

If your ISP does not support IMAP, you can either demand it or switch ISP.

Here is a list of ISP's that support IMAP.

More IMAP resources.

The original IMAP author is Mark Crispin. (I borrowed the headline of this page from his personal homepage).

He is a staff member of the University of Washington where he preaches IMAP to the world. For example, imap.org (The IMAP Connection) is hosted by the university.

Discussions on IMAP take place at comp.mail.imap

IMAP RFCs and Drafts can be found here.