Nobody can stop you from using the same email address (ie identity) on a different mailing list.
I remember there being an attempt to make implement chat using the IMAP protocol. I'm blanking on the name of it.
If you use an address under someone elses domain, they can. If you use your own domain, you can do that in the fediverse too - with the caveat that with email both range of offerings to do this without selfhosting and technical portability are better. (although the fediverse side of things hopefully will improve)
> I remember there being an attempt to make implement chat using the IMAP protocol.
Deltachat
I suppose that's true. Google can ban a gmail account that is inappropriate on a Google Groups list, or a university can ban a student's account that represents the university inappropriately. Those are narrow cases, though. It's not in the same ball park as a mod deciding to ban someone. An instance for just the account seems the best option, but I don't know the devs' intentions.