Can I disagree that Sophos is the best of all virus scanner?
I tough same thing so I have installed Sophos free in my Company Nethsecurity (NG 6.9 at the moment) in parallel with ClamAV.
ClamAV detects 99% of mail with viruses.
Rarely Sophos and ClamAV detect both the same viruses in mails.
Sophos never detects alone mails with viruses.