[Mimedefang] Non-routable addresses in HELO

Jim McCullars jim at info.uah.edu
Mon Jul 10 10:17:08 EDT 2006

On Sun, 9 Jul 2006, Dirk the Daring wrote:

>      Obviously, if I have sending hosts on my network that really did have
> non-routable addresses, this would be a possible problem (altho the simple

   I just reject when someone sends an IP address as a HELO, and it is not
their actual IP address.  In filter_sender():

  if ($helo =~ /^\d+\.\d+\.\d+\.\d+$/) {  # looks like an IP
    if ($helo ne $ip) {
      return('REJECT', "IP address $ip doesn't match helo string $helo");

  This is fairly effective, I grepped my syslog file on one of two email
relays and since last Friday it stopped over 5000 email attempts.  It has
the added effect of stopping those who use *my* IP address as the HELO


Jim McCullars
University of Alabama in Huntsville

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