Recently, whenever I logged in over SSH, the CPU load averages were always above 2. A look at top showed them well into the tens…
Most of the resource-hungry processes belonged to the postfix user, so it was clearly the culprit.
I checked in webmin and found over ten thousand spam messages in Postfix's mail queue… That was where all the resources were going…
That gave me quite a scare… I thought my account had been compromised… But then I discovered that my SMTP server wasn't using authentication at all…
Here's an SMTP authentication testing site, for future reference…
Just search Baidu for SMTP authentication and such… There are plenty of tutorials…
I guess I can't afford to cut corners on security next time. I wonder whether mail providers will end up blocking this whole IP range…