This month has been busy with CLAMAV disturbances to mail flow. Problem was verified by tailing the /var/log/maillog file on any of the 3 MTA’s and seeing entires related to “camav-milter.sock” file being locked due to permissions, or “NOQUEUE: milter-reject” entries due to memory issues.
We are attempting to solve the milter issues by croning a reload of clamav-milter daily to free up some memory. If that fails we will give servers more RAM.
The Permissions issue was solved by editing the /etc/clamav-milter.conf file to ensure proper file permissions on the sock file.