I think a forum account is the only way to go especially in this instance where YahooGroup list needs a subscribing member to email to. I think it could be made to work in such a way where, Group -> Forum, the messages are all posted from the single YahooGroup mailing list ForumId, BUT each post holds the FROM name of the original poster on Yahoo even though they are really the same "Forum" account. Perhaps some time later as users join the forum those posts could be "claimed" by the new user by doing some manual work in MySQL. And then Forum - > Group, the posts would have to all be from the single YahooGroup subscribed account, "forumdotcom", but perhaps they too could have some forum member identification in them as well if not even just an added message body header "FROM: forummember via forumdotcom."
I'd like to see something like this working. I've been wanting to add a sync forum to a few of my niche forum sites to include related activity from YahooGroups that many members participate in already. I think a catchall is a very important piece to this kind of mechanism anyway because even in a perfect setup eventually something wont be in sync and it would be tragic to lose the data along the way because of it.
M2F was going to be the way to go but I think they failed by the ridiculous amount of effort to redesign and add all of the feature creep. Step one should have just been modding existing system to work with pbpbb3 just to please a lot of people instead of the actualized result of killing them off. ...sigh.
What do I have to do to accomplish this? Can I throw some cash at someone just to get the result I need?