qpsmtpd/plugins/require_resolvable_fromhost

use Net::DNS qw(mx);

sub hook_mail {
  my ($self, $transaction, $sender) = @_;

  return DECLINED
        if ($self->qp->connection->notes('whitelistclient'));

  $sender->format ne "<>"
    and $self->qp->config("require_resolvable_fromhost")
    and !$self->check_dns($sender->host)
    and return (DENYSOFT, 
                ($sender->host
                   ? "Could not resolve ". $sender->host
                   : "FQDN required in the envelope sender"));
  
   return DECLINED;

}


sub check_dns {
  my ($self, $host) = @_;

  # for stuff where we can't even parse a hostname out of the address
  return 0 unless $host;

  return 1 if $host =~ m/^\[(\d{1,3}\.){3}\d{1,3}\]$/;

  my $res = new Net::DNS::Resolver;
  $res->tcp_timeout(30);
  $res->udp_timeout(30);
  return 1 if mx($res, $host);
  my $query = $res->search($host);
  if ($query) {
    foreach my $rr ($query->answer) {
      return 1 if $rr->type eq "A" or $rr->type eq "MX";
    }
  }
  else {
    $self->log(LOGWARN, "$$ query for $host failed: ", $res->errorstring)
      unless $res->errorstring eq "NXDOMAIN";
  }
  return 0;
}