Amavis will tag the subject line of any email that it can't scan with the tag UNCHECKED.
First check and see that the ClamAV daemon is running properly. See: How can I check the status of ClamAV and fix any problems?
Password Protected Archives
Amavis will prepend to Subject (for local recipients only) if mail could not be decoded or checked entirely, e.g. due to password-protected archives.
To Disable the UNCHECKED Header (Not recommended)
To disable this on Centos/RHEL edit the file /etc/amavisd/warden.conf or on Debian/Ubuntu edit the file /etc/amavis/conf.d/99-warden and add the line (before the last line 1;):
$undecipherable_subject_tag = undef;
After making the changes restart Amavis:
// Centos/RHEL/CloudLinux/AlmaLinux systemctl restart amavisd // Debian/Ubuntu systemctl restart amavis