> md_check_against_smtp_server
> to verify email addresses ahead.
> This works fine for 1 destination server but in some environments there
> may be a number of servers available to authenticate against, an MS
> Exchange network for example may have multiple Hub Transport servers.
> Has anyone managed to extend this excellent logic, which works perfectly
> for single MX, to allow for multiple MX ?
Here are some excerpts from my own code (my complete code
includes local caching so I don't check back too often for
the same address - I don't show that here). I assume that we
run the back-check only for mail being delivered locally, not
for mail on its way out. You'll need to configure the $EC_*
variables suitably for your installation, of course.
# Configuration: our MDAs, that we're willing to check users against:
$EC_check_against_these_mdas = '(?:mail\d+\.encs\.concordia\.ca)';
# A known valid sender address that we'll use for the checks:
$EC_checker_sender_addr = 'mail-check-b...@encs.concordia.ca';
sub concordia_check_against_smtp_server()
{
my ( $envsender, $rcpt_addr, $rcpt_mailer, $rcpt_host ) = @_;
$returnval = 'CONTINUE'; # default case: fail open
# If this isn't for SMTP delivery, cannot perform this check:
return($returnval) unless (lc $rcpt_mailer) =~ /^e?smtp$/ ;
# If a mailertable is in use, the $rcpt_host may be a list, so split
# it as needed before running any checks.
# We will check only against our own relays:
#
{
my ( $host );
@rcpt_hosts = ();
foreach $host ( split /:/, $rcpt_host )
{
$host =~ s/^\[(.*)\]$/$1/; # Strip square brackets if any.
next unless lc($host) =~ /^$EC_check_against_these_mdas$/ ; # Just ours.
push @rcpt_hosts, $host;
}
}
# If none of our relays were listed, we don't check:
return($returnval) unless @rcpt_hosts;
# Check the recipient with the next hop for this message. The first
# definite answer (if any) is used. IMPORTANT: use a known good
# sender instead of the real message's sender, otherwise a rejection
# due to a bad sender could get cached as a rejection for the
# recipient address! (RT#242833, 2012-04-27)
foreach $check_mx ( @rcpt_hosts )
{
my $query = $res->search($check_mx);
# Paranoia: run only if host exists and can be resolved:
if ($query)
{
my ( $mdc_retval, $mdc_msg ) =
main::md_check_against_smtp_server($EC_checker_sender_addr,
$rcpt_addr_noplus, $thishost, $check_mx);
if ( $mdc_retval eq 'REJECT' or $mdc_retval eq 'CONTINUE' )
{
# definitive answer, return immediately:
return($mdc_retval, "$mdc_msg (via $check_mx)");
}
# else, an error occurred, so carry on with foreach loop:
# another MDA may be available to check this user.
} # if the host resolves in DNS
} # foreach check_mx
return ($returnval); # default is CONTINUE
}
Hope that helps.
Anne.
--
Ms. Anne Bennett, Senior Sysadmin, ENCS, Concordia University, Montreal H3G 1M8
a...@encs.concordia.ca+1 514 848-2424 x2285
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