I have actually argued for the use of mailing lists for corporate engineering discussions. When that becomes the medium for code review or design discussions, there's a nice streamlined workflow. Further, it's practically trivial to write or customize a mailing list reflector. If you have a decent and secure mail client library, you're a weekend away from it just working. Contrast that with customizing or rolling you…
Fortunately there are IMAP shared mailboxes, which we worked incredibly hard at CMU during the Cyrus project to ensure would work just as well as bboards did in CMU’s previous Andrew Mail System. (“Bulletin boards,” aka bboards, were basically CMU-local Usenet, with global Usenet under a netnews.* hierarchy via a gateway.)
Most IMAP clients worth their salt support shared mailbox hierarchies, even Apple Mail does, so it’s “just” a matter of setting up shared groups on a server.