InformationWeek
Defining The Business Value Of Technology
October 12, 1998
Net Mail Scales Up
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This presents three distinct problems: the need for additional disk space, quota management, and improved server performance. Though the typical POP server may require an average of 1 Mbyte of spool space per user, plan to offer at least 10 Mbytes on IMAP servers. This extra space is needed not only for incoming or unread messages, but for folders for storing previously read messages as well. Servers should also include some type of quota-management feature, such as giving the administrator the ability to create hard or soft limits on disk space or to set default expiration times for old messages.
While POP operates on demand when users access their mailboxes to download messages, IMAP essentially creates a persistent connection to the server--messages are read incrementally and stored on the server, unless copied to a local folder on the user's desktop.
In addition, functions such as server-side folder searches place additional processing loads on the server. Higher IMAP model demands on memory and CPU utilization are a particular challenge with nonmultithreaded Unix IMAP daemons, which may spawn a separate server daemon for each active IMAP user.
IMAP Server
The cornerstone philosophy of a standards-based protocol is ubiquitous support for various clients and servers. Because IMAP4 is a standard protocol, it provides a range of client and server applications. However, IMAP only recently has become the de facto Internet mail-access protocol, so we recommend implementing a server that supports POP3 as well. Also, if you're implementing either a standalone IMAP server or an IMAP gateway to an existing legacy mail system, make sure your mail server includes an SMTP MTA that can accept incoming Internet mail and route outgoing messages to the Internet independently. Don't be fooled by a product that claims SMTP support but requires an external SMTP server (usually a Unix server running Sendmail) to route messages through the Internet.
Also consider the way the mail server integrates into your existing network infrastructure. An Internet mail server needs up-to-date user information to verify incoming addresses as well as to authenticate users logging in to check their mail. Ideally, the mail server should be able to query your existing network user directory--such as a Windows NT domain, Novell Directory Servicestree, or Unix-based Network Information Services map--unless, of course, you prefer managing yet another user database on your network. This also has implications if you're setting up a corporate address book, usually through a Lightweight Directory Access Protocol server. Products such as Netscape's SuiteSpot integrate back-end user authentication into their LDAP directory services; this also provides a white-pages service to internal and external users. However, some mail servers include their own user directories, particularly proprietary products. If this is the case, check to see if the product includes an LDAP-compliant server to publish address books.
If supporting thin clients or large populations of roaming users is a factor, try examining Web-based mail clients. Although not IMAP-standard per se, some servers include an HTML or Java-based mail reader, allowing users to read mail regardless of which desktop platform they run. Sites supporting large numbers of roaming users may consider offering universal access to users' mailboxes via the Web. You may wish to choose a server that supports Secure Sockets Layer-encrypted Web sessions to ensure the confidentiality of user passwords and message content.
Server Management
Though protocol support, integration, and scalability are critical factors in choosing an IMAP server, management features should be your next concern. Management interfaces range from plain-text configuration and log files on some Unix implementations to attractive Windows GUI applications. Regardless, some sort of remote-management capability is critical, especially on Windows NT servers. At present, Web-based interfaces are becoming the norm, and they usually have either HTML- or Java-based controls. However, Windows-based remote-management programs or a simple telnet interface may serve your needs.
Because IMAP allows users to keep their mail archives on their local mail server, managing server resources is a critical issue. Any site supporting more than a handful of users should insist on mandatory enforcement of message quotas and expiration.
In addition to disk-space management, mail servers should support some type of message filtering to help prevent spam from cluttering users' in-boxes. Some servers offer plug-in interfaces to support various agents, such as antispam filters or virus scanners. At the high end, policy-enforcement servers such as Worldtalk Corp.'s WorldSecure Server can scan message content and enforce rules for digital signatures and message encryption, but you may require an external service, like that of an SMTP relay agent, to get this capability.
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Read sidebar stories, "IMAP Searches For Its Place" and "An On-The-Road Protocol."
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