Having email participation is interesting, but it should be configurable by forum.

I have forums where I want to send email to subscribers containing the contents of messages posted, however I want them to have to come back to the site to participate in the discussion.

I also have forums where participation by email would be great in both directions, and the forum would act principally as an archive.

I bought vBulletin in the first place because I did not want to just run MailMan mailing lists and MHonArc list archives on my site. I could have done that without spending a dime on vBulletin...