On Sep 13, 13:05, Bill Bradford wrote: reject-mailhosts-with-bad-dns Um, not necessarily. You mis-typed the IP address on the second lookup. subatomix.com is indeed a valid domain name, registered by Tierranet whose nameserver (ns1.domaindiscover.com) will give you the A record and MX record for subatomix (both point to 24.94.226.65). However, there's no necessary correspondence between the domain name registrar, DNS provider for forward lookups, and ISP who provides the actual connection and address (usually also the DNS provider for reverse lookups). The reverse lookup for 24.94.226.65 comes out as okc-94-226-65.mmcable.com which isn't surprising. The reverse lookup is done by the mmcable servers, since they own the address space. If you look at Jeffrey's home page, it's URL is http://home.mmcable.com/xoraxax/, so that fits. Whether your mailserver will accept mail directly from Jeffrey's machine probably depends on what his machine is calling itself in the HELO and whether your mailserver does a reverse and forward lookup to check (as you've implied). If so, possible solutions are (1) turn off the double check, (2) have Jeffrey's machine give its mmcable.com name when sending mail, (3) have Jeffrey's machine relay mail through mmcable's server (assuming mmcable really is his ISP), or (4) persuade mmcable (again, assuming they're his ISP) to include his properly registered domain name in their DNS. -- Pete Peter Turnbull Network Manager University of York