Created a virtual host in virtualmin just with mysql, postgresql and webmin login. Then created 2 subservers.
User logged into webmin, clicks on SpamAssassin Mail Filter and just sees:
The SpamAssassin local configuration file or directory /etc/webmin/virtual-server/spam/12323558481443/virtualmin.cf was not found on your system. Maybe SpamAssassin is not installed, or your module configuration is incorrect.
where 12323558481443 is the main virtual server, created as described above.
The 2 subservers have mail, spam and virus filtering but it cannot be edited for a normal user in webmin/virtualmin.