Bulkmail ethics is somewhat simple, and I'll resume it for you in the following rules:

1. don't

Yeah, that's it. E-mail and telephone are for _personal_ or _work_ communication, about _personal_ or recipient-work-related issues, and even so limited ones (you want to reset your password? when can you come to the branch to talk about your debt? can you go to Satriani's show August 1st -- may I try to get some courtesy tickets? how is the problem in module CI027 progressing?)
Anything other than that should be handled by specific mail lists, newsgroups or (preferably!!) RSS feeds.