[Mimedefang] Forged Sender Checking

[Lucas Albers]

Jeremy Mates said:
Your code is awesome.
Implemented it on my server, and it appears to be working great!
Always interesting to see how people do things slightly differently,
code-wise.
Seems to add 3-4 seconds on a mail delivery.
So I greylist and then do a email_is_forged lookup.


made some minor improvements to your code:
adding logging if dns lookups fail.
added timeout on dns lookups.


sub email_is_forged {
my ($sender, $ip) = @_;
my  $timeout = 1;

my ($domain) = $sender =~ /\@([\w.-]+)[>.]*$/;
return 0 unless exists $forged_domains{$domain};

my $mx = $dns->query($domain, 'MX');

# TODO if no MX use the A of domain
if (!($mx)){
      md_syslog('warning',"email_is_forged,query failed: $res->errorstring
\n");
}
return 0 unless $mx;

for my $rr ($mx->answer) {
next unless $rr->type eq 'MX';
my ($result, $msg) =
md_check_against_smtp_server('<>',
$sender, 'cs.montana.edu', $rr->exchange);
next if $result eq 'TEMPFAIL';
return ($result eq 'REJECT' ? 1 : 0);
}

return 0;
}



-- 
Luke Computer Science System Administrator
Security Administrator,College of Engineering
Montana State University-Bozeman,Montana