Also of interest to the Internet messaging world is the quickly developing body of standards for calendaring and contact management. vCard, already widely deployed through clients such as Microsoft's Outlook Express and Netscape Communicator 4, presents a format for describing contact information in a message attachment or flat text file. Its cousin, vCalendar, specifies a way to exchange scheduling information, such as free/busy times, between personal information managers. More volatile is the work on iCalendar, a set of Internet drafts specifying how to facilitate full-scale interoperability between calendaring servers across Internet protocols. iCalendar, still evolving as an IETF standard at press time, will specify not only common data formats, but also peer-to-peer and client-access protocols for Internet calendaring.

Finally, the Internet world has taken steps toward supporting unified messaging through standards for Voice Profile for Internet Mail (VPIM; RFCs 2425-2426) and fax (RFCs 2301ý2306) that specify formats and MIME extensions for handling fax and voicemail via SMTP/MIME.

Directory Services: Keystone to Enterprise Messaging Directory services are like a fusion reaction--they're useless until they reach a critical mass. Though nearly every network operating system and messaging service depends on its own independent directory to store user and configuration information, the promise of a single, unified enterprise directory appears tantalizingly on the horizon.

Networks now support multiple directories from each NOS and messaging vendor. The respective technologies have improved the scalability of each system beyond a single server by sharing common user, policy and configuration information. But directories form vendor-specific islands within the network. The next step toward directory paradise is either to consolidate these directories into a single enterprise directly or synchronize attributes between each directory.

Messaging has become the driving force behind enterprise directory services. While major NOS vendors jockey for the title of enterprise directory service, messaging systems are already deploying white-pages directories throughout the enterprise. These global address books offer mail routing and addressing resolution, represent organizational and contact information about existing users, and act as a repository for digital certificates used in messaging security. A large part of coexistence with legacy messaging systems is directory synchronization, which is a major function of both message switches such as Wingra's Missive and so-called metadirectory products such as Zoomit's VIA.

The darling of the industry, LDAP (Lightweight Directory Access Protocol), has been billed as the common ground between all directory services. Indeed, we're hard-pressed to find a directory today that isn't LDAP-accessible. In the general scheme of enterprise directory services, LDAP is little more than an agreed-upon access protocol. More important issues concerning the representation of common network objects such as servers, printers and network applications in a common schema will keep directory services in the news for years to come (and will line the pockets of metadirectory vendors like Zoomit that can attempt to translate between vendor-specific schemata).

However, in the messaging world, which originally expected X.500 to deliver enterprise directory services, the wide acceptance of LIPS (Lightweight Internet Person Schema) has made a bare-bones schema for white-pages attributes such as contact, organization, certificate and contact information relatively standard. Some uncertainty persists among LDAP implementations about how to present some white-pages schema elements (current LDAP clients often confuse home and work contact information), but this is trivial compared with the plight of NOS vendors trying to standardize directory schemata.

As LDAP undoubtedly will dominate the client side of directory access--particularly throughout the messaging world--keep in mind that mail servers will now be directory clients. But the backend enterprise directory is in a state of confusion. NOS vendors will use their messaging products as a key selling point for their enterprise directory strategies; Novell's GroupWise already leverages NDS for all administrative functions, as well as user information.

Directory purists will note that GroupWise doesn't integrate directly into NDS. Rather, it periodically hashes directory information into local catalogs on the messaging server for performance reasons. Microsoft's current NT 4.0 domains offer little directory functionality, forcing current implementations of Exchange to support a proprietary directory service. Exchange won't become a full-fledged directory client until its next version (code-named "Platinum") ships, three to four months after NT 5.0.