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Q181036: INFO: Suitable Applications for Exchange Server Event Scripting

Article: Q181036
Product(s): Microsoft Exchange
Version(s): winnt:5.5
Operating System(s): 
Keyword(s): kbusage
Last Modified: 29-JUL-1999

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The information in this article applies to:

- Microsoft Exchange Server, version 5.5 
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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.

- The Event Service is single-threaded. No matter how many scripts are
  registered, only one can run at a time. The performance consequences are
  substantial. For example, a script that requires two seconds to execute, only
  allows one script to execute every two seconds, for a maximum of 30 scripts
  per minute. At that rate, 600 scripts would require 20 minutes to process.

- 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

Additional query words:

======================================================================
Keywords          : kbusage 
Technology        : kbExchangeSearch kbExchange550 kbZNotKeyword2
Version           : winnt:5.5
Issue type        : kbinfo

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