It was the blocking of mx.umich.edu
I use SPF and DKID, the arpa or "rDNS" name has never been a good method for deterring SPAM. It only is used by those that do not understand SPAM and have heard "it's a good way" to knock it down. Now, the blocking of "dynamic" IP Address ranges is a position I am torn on.
In any case, blocking based on no arpa is wrong and very stupid.
In this particular instance it choked on the mx.umich.edu IP address being listed in a blacklist. My machine handed it off to umich completely. It was bounced on choking on the listing.