I'm actually the user that's getting pissed off our company has left groups open and all the spam is now coming through

Well, sounds like someone made a mistake somewhere in cc-ing the group addresses into a public medium, but a bigger mistake may have been made earlier in the process. If I really wanted e-mail groups to be private, I'd construct them on top of a private, not-publically-reachable DNS/domain, say "thoseblokes@inside.mycompany.com" instead of "thoseblokes@mycompany.com". yes, more planning, hardware and stuff, and some limitations, but probably less aggravating over the long haul.