How can we add a disclaimer to external email messages without adding the same disclaimer to internal messages? We've tried creating an event sink, as described in the Microsoft article "HOW TO: Add a Disclaimer to Outgoing SMTP Messages in Visual Basic" (http://support.microsoft.com/?kbid=317327), but it adds disclaimers to all messages.
For less than $150, you can get a supported commercial product such as Franz Krainer's DisclaimIt or Direct Communication Software's eXclaimer2000. That's a small price to pay to avoid having to support the code yourself. No matter which solution you use, you'll have to be careful about where and how you set it up. The easiest way to prevent disclaimers from appearing on your internal messages is to set up whatever disclaimer tool you plan to use on your external bridgehead, not on your internal servers. You can set up a separate SMTP Virtual Server for outbound-routed traffic, then apply the disclaimer to messages passing through the server.