I am just stating my opion (obviously) but i dont think its harmful if you send him a friendly-no expectations email... better to be friendly than not. I understand the whole cake eating thing, but at the same time, why not make things between you somewhat positive. Doesnt mean you are asking him to be your friend... or saying you will support his A. Sorry, maybe those who know better about H's and A's have better reasoning.
I have a hard time with do I act like myself and be friendly or do I become bitter and go against my own morals and personality just to teach H a lesson. I personally prefer the first option, although I get tempted to do the latter at times.
I think as NM said, just dont expect anything back but a lighthearted response. and she has good points about keeping things civil since he is the baby's father.
Now if only MWD wrote a chapter about DBing when PG? Hmmm?