don't get. i own mydomain.com,even if i point mx to whatever.wherever.com, if spam comes from mydomain.com, why is it not my problem? i guess some of the parties warned by the likes of spamhaus/spamcop would be postmaster@mydomain.com, the mail hosting provider of whatever.wherever.com, the isp who owns the originating ip of the spams, and finally possibly the dns provider of mydomain.com. i do wonder if they look at the reply to or the from address. both?