Spam is bringing our server down....

[thunder@]

Its out of control. Our ISP shut our dedicated down becuase they said we where sending spam, turns out we where not, it was QMail just bouncing message (spam sent to our site) because of filled mail boxes. Now we are getting brute force dictionary spam to nonexistant email address. QMail sends them back to the orgination with a message saying that the account isnt active, problem is it included the original spam message, so the receiving server can interpret it as spam coming from our domain, especially bad if the domain it was originally sent from was spoofed, and it goes to someone unsuspecting. What can we do to control this? We cant ourserver doing this every time a mailbox is filled. Any sugguestions?

 

[SecondPhase]

reject non existant users

Hopefully you have a newer Plesk and Qmail, In Plesk Admin under the domain -> mail -> preferences you can change the delivery preference for non existant users to a domain.

Select between: bounce, deliver to mailbox, or reject.

Good idea to choose Reject.