Just to clarify what you're asking, here's a use case:

I was a volunteer Clerk of IT for a religious group that conducts business on-line but mostly by stowing information at a website, with all the headaches of managing logins to control who gets to post where.  Drupal.

My recommendation was we imitate Python.org a lot more by setting up mailman listservs with varying degrees of visibility to the public (some are members only and so on).  I set up a Google Group by was of demonstration and ran it for a couple years.  It's still out there.

The advantage of mail-lists are not only are they searchable but they maintain the context and threads of conversation, great for organizational memory. However, for historical reason, our clerks prefer to use conference calls in real time, with someone taking minutes for the archives.  A lose a lot that way.

There's lots more listserv use since my tenure ended, by various interest groups, but no centralized place at the regional level for these listservs to go, which is probably just fine (we're pretty informal), however I never did find how I could get mailman servers installed at our ISP, back when I was filing reports and proposals.

Our ISP only offered ancient majordomo as a listserv option, with precious little information on how to set one up.

How does one set up a bunch of domain-name specific mail servers ala Python's mm3, is that in the ballpark of what you're asking?

Kirby