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Enterprise messaging is experiencing unification and growth. The consolidation of legacy systems--driven primarily by TCO (total cost of ownership), management, functionality and Year 2000-compliance issues--marks the twilight of venerable host-based systems such as PROFS and SNADS, as well as LAN-based systems such as cc:Mail and Microsoft Mail. At the same time, the explosive growth of Internet messaging has driven SMTP to become the de facto interdomain mail-routing protocol.

Also, near-ubiquitous support for POP3 and IMAPv4 mail access protocols has opened the desktop to third-party clients, while new classes of users get corporate mailboxes, reflecting the growing dependence on electronic messaging for business communications. Your IT department is rapidly moving down a transitional path toward becoming an ISP--which makes support for Internet messaging a critical factor in your enterprise messaging deployment strategy.

Clearly, what had been tactical and departmentalized decisions are turning into more strategic investments in enterprise messaging. At this level, current messaging technologies follow two major tracks, with numerous feature sets.

Proprietary groupware vendors continue to promise value-added applications out of the box, including calendaring, scheduling and collaborative discussion groups, as well as fully featured application development environments. While Internet standards raise the functionality bar on the client side, don't expect to give up proprietary clients on the desktop if you intend to support any of these value-added functions. But if simple e-mail is your strategy, nearly universal support for SMTP/MIME, POP3, IMAPv4 and LDAP among major client and server vendors offers convincing choices for Internet standards inside the firewall--both in messaging infrastructures and on the desktop.

SMTP/MIME is a well-supported inter-MTA message- routing protocol. However, proprietary systems are still forced to maintain their own replication protocols to handle non-message traffic, such as shared folders, custom application and calendaring/scheduling propagation. Lotus, Microsoft and others claim that many of these routing functions soon will support SMTP/MIME encapsulation.

Standards: The Way of the World While SMTP/MIME's dominance throughout the Internet is undisputed, X.400 mail-routing infrastructures still exist throughout Europe. They're also found in the Defense Message System (DMS) specifications put forth by the U.S. Department of Defense, which intends to upgrade its messaging infrastructure, security and reliability using X.400 MTAs and a distributed X.500 directory.

With the addition of minor protocol enhancements in ESMTP such as multinational character-set support, 8-bit MIME transmissions and message-size declaration, SMTP's functionality is expanding. But it still lacks functions found in other message transfer protocols, including delivery and read receipt notifications and message retractions/cancellations, though many such features are in the chute.

SMTP delivery status notifications (DSNs), which allow mail clients to request a "success" or "failure of delivery" notification from remote MTAs, are defined in RFC 1891, and are included among ESMTP's functions.