I have been struggling with this forwarding issue in a slightly different manner: any messages I try to manually forward from my iPhone just never arrive to the intended recipients. I have tested this on multiple occasions and to multiple e-mail addresses.
Using a .mac account via icloud now, I can "reply", create a new message from my iPhone and it gets right through. Using iCLoud on my Mac deskop, forwarding works just fine (again, using my .mac handle). Would love to hear of any solutions to this issue.