IMAP secrets — what you need to know

By Paul Thurrott

Sometimes described as the best-kept secret on the Internet, the IMAP e-mail protocol might more accurately be thought of as “Exchange Server for the rest of us.”

IMAP, which stands for Internet Message Access Protocol, is a more modern protocol than POP3 (POP stands for Post Office Protocol). POP3 is far more commonly used, but is also far less versatile.

POP3 more or less assumes you will only access your e-mail from a single machine. When you check a POP3 e-mail account, your mail is typically downloaded to the PC and the messages are then removed from the server.

In this sense, POP3 is essentially a client-side e-mail solution. But if you experience any problems with the client machine, your e-mail data could be lost forever because the server-based copies were deleted.

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The benefits of IMAP over POP3
IMAP is a superset of POP3. For example, both standards support offline mail access and are based on open standards.

But IMAP offers many advantages over POP3.

First, it’s a server-side solution, similar to Microsoft’s proprietary Exchange Server. Your mail store is maintained by an Internet service provider (ISP), or a Web server you manage, that supports IMAP. You can then access your e-mail from any location — home, work, an Internet terminal — and not have to worry about permanently downloading messages. This arrangement also lets you access the same IMAP mailbox from multiple machines at the same time.

IMAP also saves bandwidth by only downloading e-mail message headers — and not the entire message — until you select individual messages. This is also handy for manual spam filtering. If you see a message you know is spam, which might contain dangerous content, you can delete it before the message body is downloaded to your client.

If you want to read your e-mail offline, however, you can optionally download a copy of each IMAP message locally. This is especially handy if you want to respond to e-mail when you’re going to be offline for a while.

Server-side management vs. client-side
IMAP is more versatile than POP3 in other ways as well. For example, you can create any number of server-side hierarchical folders to better organize your e-mail.

This is particularly useful for spam filters. Such filters often move suspect mail into special folders, which you can check like any other e-mail folder.

Furthermore, IMAP folders can be individually configured, using the proper e-mail client. You might specify which folders the client should poll for new e-mail on a regular basis. Using POP3, you can typically only check your local Inbox folder.

IMAP’s feature set makes it a perfect solution for people who use multiple PCs and don’t want to have to worry about where certain batches of e-mail are located.

It’s also excellent for mobile users, including Blackberry and PDA users, who like to check e-mail from non-PC clients and keep it all synchronized. When you mark a message as read from one client, it’s marked as read on all clients that hit the IMAP server.

POP3 still rules the behavior of most downloaders
Given these and other advantages, it’s unclear why IMAP hasn’t unseated POP3 as the dominant e-mail type. We have a few theories.

First, many e-mail users are now utilizing Web-based e-mail servers, such as Hotmail and Yahoo Mail. Services with this design are easier for ISPs to host and administer. Webmail is actually pretty convenient, and offers many of the server-side benefits of IMAP. But only some Webmail accounts are accessible via dedicated e-mail clients, which limits their usefulness.

Second, corporate users are increasingly turning to Exchange. This program is supported by the world’s largest software company, which is more interested in pushing its own proprietary solutions than open standards like IMAP. (Ironically, Exchange does support IMAP, but Exchange is a resource-heavy server with complicated administration requirements).

Ways to improve on the IMAP protocol
IMAP isn’t perfect, of course, and it may require some training if you’re used to POP3 e-mail.

Our biggest complaint is the “delete” model. When you delete an IMAP-based e-mail with most e-mail clients, the e-mail isn’t actually deleted, but is rather marked for deletion. To actually permanently delete, or purge, that e-mail, you’ll need to take an extra step. In Outlook, you can permanently delete e-mail that’s been marked for deletion by choosing Edit and then Purged Deleted Messages. This may not be obvious to many people.

Many e-mail clients, including Outlook and Outlook Express, have IMAP capabilities but support IMAP poorly. As a strong new contender for the e-mail crown, the 1.0 version of Thunderbird, a standalone e-mail client, which offers excellent IMAP support, was recently released by the Mozilla Foundation.

A Microsoft developer raves about Thunderbird and Entourage
Even Microsoft’s Omar Shahine, a lead program manager on the Hotmail Front Door team, recently described Thunderbird as “almost the perfect client for IMAP.” He gives Outlook Express a C and Outlook a D+ for their IMAP support. Thunderbird rates a B+, whereas Microsoft’s Mac-based e-mail client Entourage — which Shahine himself developed the IMAP support for — not surprisingly rates an A- for that capability.

Now that it’s finally released, we’ll be testing Thunderbird over the coming weeks and publishing our findings.

Unless you’re using Exchange Server, which offers similar features to IMAP — albeit with heavier system resource requirements and addition collaboration options — you should really look into IMAP. There’s little doubt that e-mail is the “killer app” of the Internet. But so many people are hobbled by the limitations of Webmail or POP3 mail that e-mail has become more drudgery than convenience.

How to get started with IMAP
You can learn more online about the design and goals of IMAP. Some good resources include the IMAP Connection, an excellent introduction to the topic, and Infinite Ink, a site that maintains a gigantic list of IMAP-compatible service providers.

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