Having worked on TA's for a while now we've found there are several things missing in the object model for our requirements. Consequently we have some horrible code that need to do some things directly either with MIME or TNEF - which is a crying shame as MS must have all the code to do the things we need anyway, it's just that the object model is deficient.
It'd be useful if there were an Exchange category on MS Connect where we could submit our suggestions, but as far as I can see, there isn't one.
So, where do the Exchange TA developers get to hear customer feedback?