Cool, I'll spend some time reviewing those utils.
It's a one-way list, so the only incoming mail is stuff we don't want. What I was most concerned about is there are several email aliases related to the list, which I don't quite understand. I recall from my previous linux experience (in the '90s) that we had to manually set up email aliases in an alias for ListServ lists when we did something like this with them. MailMan sends from a SENDER: address of list_name-bounces@domain.com. I have no alias for that set up, but I don't see one on the client's current Plesk, either. The REPLY-TO: address I have set up, so maybe that's all that matters. I was just worried that there was exim-related stuff that might be missing in terms of handling addresses or whatever, if all I was doing was copying list config files from his mailman path to mine. I'll look and see what others have to say about that.
Thanks again for all your thoughtful input. It's been quite helpful and reassuring.