This is good stuff...
Just for an update, MS Live Support has allegedly been working on my problems for the past few days. In the dozen emails we have traded, they say they have tried some backdoor fixes (removing the HIP challenges etc), but those haven't worked either. What stumps me more then having this issue, is that I appear to be the only one that is having problems with it. The fact that email is delivered to my phone, but gives me an error on sending makes me believe this is a T-Mobile issue (since it rejects the message well before Hotmail would have sent it back). Could that be? Are there any upgrades that T-Mobile needed to do with the new BIS 2.5 that may have been missed?
Still hopeful, but loosing faith.
Addition: I just realized that I never re-filled in the APN information under TCP. I don't know if that had anything to do with it, but I have now gotten 2 emails out of 10 to deliver properly.