Managing Messages with IMAP

Internet Message Access Protocol (IMAP) allows clients to remotely create and manipulate mailboxes on the server and to have a folder hierarchy. This gives clients better control over the way mail is organized. IMAP also allows shared access to mail folders. For example, you could set up a mailbox for the sales department for mail that is of interest to that group. Such a setup would also allow more than one clie nt to access the mailbox at once. AltaVista Mail Server doesn't support IMAP shared folders, but an add-on product called Forum serves as a bulletin board/collaborative service.

Since IMAP and Post Office Protocol (POP) both use Simple Mail Transport Protocol (SMTP), IMAP users can receive messages created with POP clients and vice versa. Be advised, though, that while it's easy to change over an existing POP mail system to use IMAP exclusively, reverting back from IMAP to POP is an administrator's nightmare. Moving IMAP folders back to POP dumps all mailbox subfol ders into a single root folder. And while it's possible to maintain both POP and IMAP mailboxes in the same mail system, this approach largely negates the reason for using IMAP in the first place.

Probably IMAP's slickest feature is its built-in database capabilities, which allow defining rules for searching, selecting, and deleting mail based on values in the message header or body. IMAP also permits s elective downloading of message parts, so you can retrieve a message without a file attachment. Some e-mail client packages also allow attaching rules to folders. Opening the server folder displays only the mail messages that meet the rule criteria. Rules allow actions to be assigned to the criteria, which helps users administer their mailboxes. For example, a rule could be set to delete all messages received before a certain date. All the server packages support searching and rules defining, but all clients do not.

The IMAP specification allows for negotiated extensions to be added to the list of IMAP's basic functionality. At present, none of the tested programs supports the access control list (ACL) extension of IMAP. An ACL allows limiting mail access by a list of IP addresses set by the mail administrator. This is similar to Windows NT's use of ACLs, but it's specific to IMAP services. Both Netscape Mail Server and TeamWare Mail offer proprietary methods of limiting access by domain names. All four programs offer password encryption of mail account log-ins using MD5 or Authenticated POP (APOP). Netscape also supports S/KEY authentication and supports Secure Sockets Layer (SSL) when using a Web browser to administer the server. None of the programs currently implements encryption of messages on the server, but TeamWare Mail offers an add-on cryptography client package.

Two other extensions that aren't supported are Quota and Annotate. Quotas let you limit the size of IMAP mailboxes and mail messages. Annotation allows groupware-style collaboration, but differences in client platforms make it extremely hard to implement.

There's a list of IMAP4 clients at http://www.imap.org/products.html . This site also includes a list of other IMAP4 servers. You can download the source code for the U niversity of Washington's IMAP4 server for free.

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TeamWare Puts You in Control

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TeamWare gives administrators full control of configuration parameters.