Majordomo

majordomo is popular mailing list software. It has mainly been replaced by mailman which is also mailing list software, but it has a web-based management UI. If you're running majordomo and you have a restricted mailing list, meaning list members need to be subscribed to post, you will most likely be getting messages that look like this:

BOUNCE [email protected]:    Non-member submission from ["Alexis Hanley" <[email protected]>]

so you can verify if it's a legitimate bounce or not (if someone changes their hostname like from @real.example.com to @new.example.com this would also bounce) and do what you wish. I've had a majordomo list for nearly a decade, and so it's on a lot of spam lists, thus I was getting a lot of spam bouncing. This was until I just came across this patch which allows you to create a non_member_bounce = variable that will send this bounces to the sender, letting them know they need to subscribe to post. This means no more administration of bounce emails for you from spammers. At least until they start subscribing to your list.