"Delivered-To" Header in Exchange

If I am understanding the question correctly, here is a way to get the headers you want, but I bet you won't like it. It is based on transport rules.

If you can control the set of OTRS addresses and they can be registered in Exchange (as Exchange contacts, maybe) then you can make a transport rule for each of them as follows:

Apply rule to messages
sent to **OTRS Username**
and set X-Envelope-To with **[email protected]**

As fmysky notes, the horrible thing about transport rules is that they take literal strings. So you would need a transport rule for each OTRS address (but you would not need one for every distribution list).

I tried this in my Exchange 2007 environment and it worked when I sent a message to one of our internal distribution lists.