The best approach for doing this sort of thing has been through third-party products, and
Exclaimer is actually a package of tools that includes archiving, antispam technology, an auto-responder module, mail blocking and redirection -- but the disclaimer function is most intriguing.
Exclaimer can add different types of disclaimers depending on whether a given piece of e-mail has been sent to the outside world or to an internal user. It also supports all manner of e-mail content, including RTF, HTML, digitally signed and encrypted e-mail, and so on.
In addition, the program lets you use any field from Active Directory as a merge field, so you can have a user's name, telephone number and other contact information added "live" from AD without user intervention.
Disclaimers can be appended or removed based on predefined rules or matches against e-mail content, which allows (among other things) the same disclaimer to not be appended several times to the same message if it's replied to and shuttlecocked back and forth.
Exclaimer costs $175 per server for Small Business Server 2003 users (antispam and support cost extra per-year fees), and at a starting cost of $245 for 25 users on a conventional Exchange server. A 30-day trial version, with all features enabled, is available from the Exclaimer site as a download.
One minor gripe I have is that it's not possible to only purchase the disclaimer functionality to the exclusion of everything else; but the antispam function is sold separately, since it may eclipse tools already in use on your Exchange server.
About the author: Serdar Yegulalp is editor of the Windows Power Users Newsletter.
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This was first published in February 2006