I had another situation where a message was looping forever, being
repeatedly delivered from my server to itself, and causing a high load.
The problem is that the MX record looks like this:
conservation.com. 3600 IN MX 1000 0.0.0.0.
I've previously encountered the same problem with other domains. Since
the message is coming from inside my network and has a local FROM
address, it's accepted for relaying. Then because of the MX record it
gets "relayed" from the server to itself and queued for relaying again
and again.
With qmail-smtpd, this wouldn't go on for long, because there's
primitive loop detection, counting the number of "Received" and
"Delivered-To" lines. But qpsmtpd is missing that.
I've attached a plugin that duplicates the loop-checking in qmail-smtpd.
--
Keith C. Ivey <[EMAIL PROTECTED]>
Washington, DC
#!/usr/bin/perl
=head1 NAME
check_loop - Detect mail loops
=head1 DESCRIPTION
This plugin detects loops by counting "Received" and "Delivered-To"
header lines. It's a kluge but it duplicates what qmail-smtpd does,
and it does at least prevent messages from looping forever.
=head1 CONFIGURATION
Takes one optional parameter, the maximum number of "hops" ("Received"
and lines plus "Delivered-To" lines) allowed. The default is 100, the
same as in qmail-smtpd.
=head1 AUTHOR
Written by Keith C. Ivey
=head1 LICENSE
Released to the public domain, 17 June 2005.
=cut
sub register {
my ($self, $qp, @args) = @_;
$self->register_hook("data_post", "check_loop");
$self->{_max_hops} = $args[0] || 100;
if ( $self->{_max_hops} !~ /^\d+$/ ) {
$self->log(LOGWARN, "Invalid max_hops value -- using default");
}
$self->log(LOGWARN, "Ignoring additional arguments") if @args > 1;
}
sub check_loop {
my ($self, $transaction) = @_;
my $hops = 0;
$hops++ for $transaction->header->get('Received'),
$transaction->header->get('Delivered-To');
if ( $hops >= $self->{_max_hops} ) {
return DENY, "Too many hops. This message is looping.";
}
return DECLINED;
}
