Disclaimer: This post is about Disclaimers...

I was reviewing a customer's case today and it reminded me of a topic I meant to blog about a while ago...

Ever since Exchange 2000/2003 customers have tried to apply the disclaimer SMTP sink sample to internal mail and found that the disclaimer text is not stamped on these messages. Of course in Exchange 2000/2003 this won't work. This is further described in the Exchange 2003 documentation on TechNet about The Advanced Queuing Engine...

"...the CDO interface does not support changing the content of store-submitted messages. This is a limitation that CDO_OnArrival event sinks share with all other event sinks. This limitation exists because Exchange converts a store-submitted message to a temporary SMTP version for the event sink to handle, and then discards the temporary version after the sink finishes processing...

...Because Exchange discards the temporary copy of a store-submitted message, you cannot use an event sink to add a disclaimer or other modifications to all outbound messages, unless you force all messages to be received through SMTP. To do this, you must install the event sink on a bridgehead server that is separate from the mailbox servers in your organization."

This is one of the better explanations about why disclaimers don't work for internal mail in Exchange 2000/2003 and provides more detail than the KB article.  What you don't get from the KB article or the TechNet documentation is that in Exchange 2007 this all changes...

The entire transport process is redone to the point that not only can internal messages have disclaimers added to them but there is no scripting or coding involved in doing so. Exchange 2007 has built in transport rules that an administrator can turn on and configure as needed without writing code.  The impact on Exchange development here is that the Exchange 2000/2003 experience leads many of us to assume that tasks like adding disclaimers, prepending text to the subject lines, adding headers, adding recipients, or redirecting messages requires code but in Exchange 2007 it does not. 

...Of course not every solution fits within the fixed set of conditions and actions defined for these transport rules - in those cases a custom transport agent can be used to implement whatever business logic is needed. However, it is important to remember this functionality exists in Exchange 2007 before setting out on developing a custom solution as to not reinvent the wheel....