I have been having problems with a domain which spammers are using in forged email headers. So I am getting returned mail form spam blockers and such to email addresses at my domain which does not exist. I have checked that the server is not compromised and changed passwords. The mail is continuing. My question is - in terms of letting the hosts receiving this spam know that the mail is not coming from my domain, what an I do? Does it help to set the catchall address to :blackhole; or :fail: no such address here? If so, which on is better? Any advice greatly appreciated.
I would suggest taking a look at the post by one of the cPanel developers http://www.configserver.com/free/fail.html