Select Settings -> Protocols -> SMTP -> Anti Virus
Click on the ClamWin tab
Select Use ClamWin
If the autodetection of the paths fails, you will have to enter the paths manually.
To test the virus scanning capability, download a test virus from eicar.
Practically all virus scanners treat the test virus, eicar.com, as if it was a real virus. The file contains a string that makes the scanners think they've detected a real virus. To test the antivirus functionality in hMailServer, attach the eicar.com file to an email and send it through hMailServer.