I know mailchimp has rss feed and rss-to-email function (apart from social functions). Maybe something like this can help as well: http://mods.mybb.com/view/rss-feed-poster
and this: https://ifttt.com/wtf
If you would use RSS to email, you can use the Forum as a rss-source.
and this: https://ifttt.com/wtf
If you would use RSS to email, you can use the Forum as a rss-source.