Hi,

Newer versions of Ubuntu enable an apparmor profile on /usr/sbin/clamd, this prohibits clam from seeing the Mailscanner spool folders and thus it cannot scan for viruses.  This issue is shown in the clamav logs as a 'permission denied' or 'access denied' error or similar, even if the permissions/groups on those folders is set correctly.

You need to edit the file /etc/apparmor.d/usr.sbin.clamd and add the following line:

 /var/spool/MailScanner/incoming/** r,

Regards,
Steve