How to change MAPI MessageClass in Exchange 2010?

Question

I am trying to get Exchange 2010 to change the MessageClass (PR_MESSAGE_CLASS) of an incoming message to that of my custom form (IPM.Note.MyCustom) when the incoming message has a certain header set. (X-MyCustomHeader: Yes)

I have seen some information about setting another MIME header (Content-Class:) that Exchange will use to set the MessageClass, but it doesn't seem to work for me. (I've seen examples that use Content-Class: MyCustom and Content-Class: urn:content-class:custom.MyCustom)

I've even looked into writing a transport agent with C#, and I did find a MapiMessageClass property on the EmailMessage class, but it's read-only. I also looked at added a MAPI property in a TNEF section, but the Exchange API does not offer a way to create a TNEF section if one does not already exist. (And most mail from the Internet doesn't.)

There's got to be a way to do this. What am I missing?

Answer 1

We do it using Outlook Remption: http://www.dimastr.com/redemption/rdo/RDOMail.htm The MessageClass property of RDOMail is Read/Write. Redemption just wraps Extended MAPI though so you could do it with native code if you don't want to use a 3rd party library.