The open-source anti-virus engine ClamAV is included in the Halon platform. It allow you to get a second opinion about viruses.
Reject("ClamAV thinks your message is contains a virus");
Skip certain signaturs
This example filter various heuristics detection from the ClamAV antivirus engine, which may be useful if these apply to you on regular basis preventing unwanted false-positives.
// ClamAV check
$skip = ["Xls.Exploit.EmbeddedFlash-1"];
$clam = ;
foreach (builtin ScanCLAM() as $v)
if (!in_array($v, $skip))
$clam = $v;