I've been using the following, though I don't recall how I obtained it. I
checked my logs (28 days worth) and it hasn't rejected anything in that
time. I haven't done any direct testing.
==========================================================================
#!/usr/bin/perl
=head1 NAME
loops - 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->{ _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 hook_data_post {
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 ;
}
