One other aspect:
There are a LOT of people searching for this feature. So far, the only hits I've gotten have either been commercial ventures, or ONE OS forum -- phorum which has modules for this functionality.
(Search google for "mailing list" forum integration.
In some of the discussions I've read, the issue comes up of the problem of spamming. Faking an email address is easy.
I can the following solution to spamming, and this would also apply to email lists.
When you sign up, you are asked for a pass phrase. Email to the list or forum must contain this line by itself in the message. Before it is passed to the rest of the list, or posted to the forum, this phrase is stripped out. When a message is sent to a user, the phrase is put in again.
If someone replies to a message, with full quote, the phrase will be there, and likely be stripped with the full quote. If somoene posts, they have to remember to put in the phrase. If they forget, the list server side returns the post, asking for the phrase.
Phrases don't have to be unique. Each userid is associated with a phrase is all.
The security is no better than the security for email. But for this use it is adequate.
Refinements: Multiple incorrect phrases are brought to the attention of moderators.