I had planned on using Google Groups, but just discovered that if you wish to use the web-based frontend to a Google Group, you need a gmail email account. This is not acceptable for the usage I have in mind.
FUDForum seems to have been abandoned about a year ago. Too bad as that was my second choice to Google Groups.
The best candidate I can find so far is mail2forum
My challenge: I have to provide an online discussion capability that allows for people that can only use a mailing list to collaborate with people who choose to use a web-based forum. They need to be able to use their existing email accounts (i.e. not forced to use a gmail or yahoo account). It needs to be 100% restricted to only those user hand-picked to be allowed to join.
The most common thing I find on the internet about this topic is several variations on, "I can't believe this hasn't been created yet!". And those comments go back to about 2001.