I think it shouldn't be a problem to get both in one. A mailing system that also get you a forum to answer that and somewhere a possibility if you want to get these e-mails or not. As sender mail there should be a mailadress with the topic number inside and you send back to the topic and he automaticly adds that to the forum.
So I like to get both.
[X] Exploder
[X] Online Forum
Best regards,
Eike