If a bulk, unsolicited, email program (spam) references your domain, you are violating our policies. This applies even if you send the spam through another email server, like hotmail.
Bottom line - do not post email or newsgroup spams that reference your site in the header of body of the post. If you are running a member type site (like a MLM program), it is YOUR responsibility to make sure the members do not use spam that references your site (or a subdirectory).