+Enable advanced filters for statistic.
++
+If this is enabled, the receiver statistic are limited to active ones
+(receivers which also sent out mail in the 90 days before), and the contact
+statistic will not contain these active receivers.
+
+`avast`: `<boolean>` ('default =' `0`)::
+
+Use Avast Virus Scanner (/usr/bin/scan). You need to buy and install 'Avast Core Security' before you can enable this feature.
+
+`clamav`: `<boolean>` ('default =' `1`)::
+
+Use ClamAV Virus Scanner. This is the default virus scanner and is enabled by default.
+
+`custom_check`: `<boolean>` ('default =' `0`)::
+
+Use Custom Check Script. The script has to take the defined arguments and can return Virus findings or a Spamscore.