Cloudlinux / Imunify360 added their own version of ClamAV to their repo which accidentally replaces the EPEL version of ClamAV required by Warden. To Fix:
You can configure Warden so that mail is still accepted when the ClamAV daemon is down. Under Warden -> Settings -> AV Milter Settings -> Actions -> Change the On fail option to Accept. Press the restart button to restart the ClamAV milter.
Remove the Imunify360 ClamAV
rpm -e --nodeps clamav clamav-data clamav-filesystem clamav-lib clamav-update clamav-server
Exclude their ClamAV packages from Yum
Add the line exclude=clam* to the [imunify360] repo section in the file /etc/yum.repos.d/imunify360.repo or /etc/yum.repos.d/cloudlinux-imunify360.repo (if they exist). After it should look something like this (do not use our example as it will vary from system to system):
[imunify360] name=EL-7 - Imunify360 baseurl=https://repo.imunify360.cloudlinux.com/defense360/el/7/updates/x86_64/ username=defense360 password=XXX enabled=1 gpgcheck=1 gpgkey=https://repo.imunify360.cloudlinux.com/defense360/RPM-GPG-KEY-CloudLinux exclude=clam*
In Warden go to Settings -> Application setup and go though the Warden Setup Wizard again to re-run the product installer (applying the default settings to the Antivirus pages) to re-apply the correct settings that were replaced by the Immunify360 ClamAV.
If you still have trouble don't hesitate to open a ticket to have a support technician fix this for you.