[Mimedefang] Can't make filter_sender from slide to work

[aNguyen]

I've got this code from mimedefang website's slide but unable to make it 
work. I've enabled sender_check and added the filter but mimedefang is dead 
shortly after starting it... I don't know if it's the filter's syntax error 
or something else... my mimedefang works fine without this addition.
I also notice that my filter does not include a sub canonicalize_email, so 
I'm working on adding it above the filter_sender.
Hope I move into the right direction.
Thanks,
An Nguyen

sub filter_sender {

my ($from, $hostip, $hostname, $helo) eq @_;

$from = canonicalize_email($from);

if ($from =~ /\@comcast\.net$/ and

!($hostname =~ /comcast\.net$/)) {

return('REJECT',

"Mail from comcast.net not accepted from $hostname");

}

return('CONTINUE', 'OK');

}