SMTP Relaying Issue

[neoform]

I was just notified by my ISP that my IP has been blacklisted.

I took a look at my logs and found millions of outgoing messages.. apparently someone has hijacked my mail server..

I've since had to shut down the server altogether until I can figure out why someone's able to do SMTP relaying..

How can I stop this relaying from happening? I was under the impression turning on SMTP auth would do this, but clearly that's not the case.

[Code Crafters]

SMTP authentication will stop all unauthorised access to relaying via your mail server. However, things that can bypass this are relaying safe IPs (same settings page) or users with a username and password logging in a SPAMing. So check your SMTP, WebMail and OutMail logs to see who's been sending mail. You should also consider setting the Max Mails Sent Per IP limits in the SMTP settings to stop any 1 IP sending too much mail in a day although don't set this too low if your logs show all mail coming from one IP (your router).