Amavis stopping

Paul R. Ganci ganci at
Wed Jun 28 03:44:30 CEST 2017

I have had the same problem which has recently begun maybe 10 days or so 
ago. I have managed to track it down to two particular emails that are 
definitely spam and have created a Amavis DoS attack situation. 
Basically the symptom appears to be that all 6 of the Amavis processes 
on the server end up taking up 100% of the 6 processors assigned for 
spam detection. The Amavis processes attempt to scan these messages and 
never complete. As a result any other email gets "stuck" in the mailq 
and hence the postifx error message that you mention appears in the 
maillog file.

The only way I have managed to fix this problem is to move all the email 
out of the Postfix mail queue, restart Amavis and then start 
re-submitting the mail back into the queue. That is how I found which 
spam emails were causing the DoS attack on the Amavis daemon. These 
emails originated mostly from Amsterdam, France and here 
in the US. I have blocked the hosts from which these emails have 
originated and have been okay since. I also have created a hourly cron 
job to restart Amavis and then flush the Postifix mailq which seemed to 
help a bit but did not completely stop the problem

What I would really like to know is what in these messages is causing 
the 100% CPU usage and the subsequent DoS situation. I have the emails 
handy if that would help but are there any suggestions as to how to 
configure Amavis to avoid situations like a combinatorial explosion (no 
I am not using my own spamassassin rules) mentioned in the other thread 
(Amavis 100%)? I would even consider a timer... Give a Amavis process a 
5 minute CPU limit and then just deliver the message is a better 
situation than having thousands of messages queued up because all the 
Amavis processes are running at 100% CPU for hours on end in my case.

I realize this is  kind of general but people might have suggestions as 
to Amavis configuration which can at least avoid the problem which 
pretty much has shutdown my two email servers twice over the last couple 
of weeks. I am also willing to provide the two culprit emails to anyone 
who might like to look them over. In the meantime I might try raising 
the debug level and running strace as suggested in the previously 
mentioned thread... in principle I just need to re-submit one of the 
offending messages. Any other ideas are welcome. Thanks.

Paul (ganci at
cell: (303)257-5208

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