======================================================================
For Postfix users:

1. Edit master.cf and put there:
filter  unix  -  n  n  -  -  pipe  flags=R user=postfix \
    argv=%%PREFIX%%/bin/clamfilter -F admin@domain.com \
    -f ${sender} -- ${recipient}

2. Add the content_filter option to smtpd binary:
smtp  inet  n  -  n  -  -  smtpd -o content_filter=filter:dummy

3. Restart Postfix.
======================================================================