XADM: Suitable Applications for Exchange Server Event Scripting

 Last reviewed: February 17, 1998
Article ID: Q181036
The information in this article applies to:
  • Microsoft Exchange Server, version 5.5

SUMMARY

Microsoft Exchange Server 5.5 Scripting Agent provides the ability to run server-side scripts in response to events that occur in folders, including private mailboxes. This article will explain why the proper application of Event Scripting is limited to medium-volume workflow and administrative applications.

MORE INFORMATION

Because the Microsoft Exchange Server 5.5 Scripting Agent permits scripts to run against individual mailboxes, many developers have attempted to write Inbox Agents in VBScript. These attempts have yielded poor results, because the Event Scripting Agent is not designed to replace traditional mailbox agents written in C/C++. Such agents are normally used to scan every piece of mail in or out of the system for viruses, or to archive every message for government record-keeping purposes.

There are several vital limitations to the Microsoft Exchange Event Service that render it unsuitable for such applications:

- There is no guarantee that a script will see every message. The Event 

   Service fires events asynchronously with respect to the Microsoft
   Exchange information store. This means that the information store does
   not block an event script (wait for it to run) before letting other
   processes or users access the folder or message. Consequently, that
   message could be moved, copied, deleted, or modified before a script has
   a chance to run. For example, a script to process all outgoing messages,
   applied to the OnMessageCreated event in the Outbox folder, may not
   react to the event before the new message has been delivered and deleted
   from your Outbox.
- Some of these types of scripting applications may face problems of 
   scale. Depending on the application's purpose, either the script would
   have to be manually installed in every folder for every user, or event
   volume would simply be too high to process with an interpreted language
   like VBScript.
- When a VB script runs for every new message arriving at a folder, the 
   performance of Exchange Server will slow to that of your script.
- Event Scripts run in a privileged Windows NT security context, that of 
   the Exchange Server service account. One grave consequence of this
   arrangement is the possibility that a script can open any mailbox on the
   server and make changes to the contents, without the owner's knowledge.
   The Exchange 5.5 Release Notes state: "The Scripting Agent is not a
   safe, general purpose replacement for the Inbox Assistant rules because
   it allows new code to be installed and run on your servers."

REFERENCES

   Microsoft Exchange Scripting Agent Help File
   Microsoft Exchange Server 5.5 Release Notes
   Microsoft Exchange Server Product Group


Keywords          : XADM XGen kbusage
Version           : WINDOWS:5.5
Platform          : winnt
Issue type        : kbinfo

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Last reviewed: February 17, 1998
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