Another necessary settings of Kerio MailServer to be done are enabling of the antivirus control and attachment filter that can be performed in the following sections:
Antivirus check can be enabled under Configuration → Content Filter → Antivirus:
Check that the Use the integrated McAfee antivirus engine option is running.
On the Kerio MailServer's host, install the external Clam AntiVirus.
Under Configuration → Content Filter → Antivirus, enable option Use external antivirus and select Clam AntiVirus in the menu.
To set attachment filter, go to the Configuration → Content Filter → Attachment Filter section and check the Enable attachment filter option.
In the list, it is also possible to add/remove other attachments to be filtered and use the button to add attachment types which are not included in the list yet.