Could just be a glitch
But it demonstrates nicely the problems of dealing with a company who will only let you do what they think is best for you. As long as you do things the Apple way all is sweetness and roses but try to deviate from it and risk the wrath of the all powerful Jobs.
I would like to think its a glitch but given that they have a track record of this kind of thing (rejecting political apps from the store that they disapprove of for example) and the fact that they are filtering your outgoing mail in the first place with no good reason to (can't think of a good reason to be filtering your outgoing mail at all) should make people sit up and take notice.