MIMEDefang filter_sender() sub not working

[Yang Xiao]

Hi guys, 

I tried to get help from the MIMEDefang list, but my posts seemed to
be invisible on there for some reason. So if any of you are a
MIMEDefang user, maybe you can help me on this.
I'm just trying to get my feet wet by adding a sample sub like this in
the mimedefang-filter file

#
# Filter Sender who says they are OHPP.COM
#
sub filter_sender {
        my ($sender, $ip, $hostname, $helo) = @_;
                if ($helo =~ /ohpp\.com$/i) {
                        return (REJECT, "goaway.");
        }
        return (CONTINUE,"OK");
}

I don't expect to ever receive incoming email from my own domain on this box.

But this is not working, any ideas?
Many Thanks,

Yang