How are you testing for this? I've been wanting to do this for a while, since my backup MX queue is always full of junk trying to be sent back...
I didn't see the original message on the list. Here's my implementation:
use Net::DNS;
sub GetHostAddresses ($$) {
my ($resolver,$hostname) = @_;
my @addresses;
my $received = $resolver->search($hostname);
foreach my $rr ($received->answer) {
next unless $rr->type eq "A";
push(@addresses, $rr->address);
}
return @addresses;
}# GetDomainMXAddresses(resolver,domain) # returns array of IP addresses for domain's MX list # if no MX records, returns array of IP addresses for this hostname
sub GetDomainMXAddresses ($$) {
my ($resolver,$domain) = @_;
my @mxlist = mx($resolver, $domain);
my @mxaddresses;
if (@mxlist) {
push(@mxaddresses, map { GetHostAddresses($resolver, $_->exchange); } @mxlist);
} else { # check for an A record for the domain...
push(@mxaddresses, GetHostAddresses($resolver, $domain));
}
return @mxaddresses;
}
# MTA_is_domain_MX(domain,address) # returns TRUE if address is a MX for domain
sub MTA_is_domain_MX ($$) {
my ($domain,$address) = @_;
return grep { /^$address$/ } GetDomainMXAddresses(Net::DNS::Resolver->new, $domain);
}
#Usage:
if (MTA_is_domain_MX($MyDomain,$RelayAddr)) {
# don't pester mx backup
return action_discard();
} else {
return action_bounce($message);
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