post-delivery virus scan

[Brad Koehn]

I have discovered that many times the virus definitions I use for scanning messages (ClamAV, with the unofficial signatures http://sanesecurity.com/usage/linux-scripts/) are updated some time after my server has received an infected email. It seems the virus creators are trying to race the virus definition creators to see who can deliver first; more than half of the infected messages are found after they’ve been delivered. Great. 

To help detect and remove the infected messages after they’ve been delivered to users’ mailboxes, I created a small script that iterates the INBOX and Junk mailbox directories, scans recent messages for viruses, and deletes them if found. The source of my script (run via cron) is here: https://gitlab.koehn.com/snippets/9

Unfortunately Dovecot doesn’t like it if messages are deleted (dbox) out from under it. I tried a doveadm force-resync on the folder containing the messages, but it seems Dovecot is still unhappy. At least on the new version (2.2.26.0) it doesn’t crash; 2.2.25 would panic and coredump when it discovered messages had been deleted. 

I’m wondering if there’s a better way to scan recent messages and eradicate them so the Dovecot isn’t upset when it happens. Maybe using doveadm search? Looking for suggestions. 




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Brad