[Mimedefang] Soliciting opinions on filtering based on bad MX records

[Kenneth Porter]

--On Thursday, September 11, 2003 3:25 PM -0500 Michael Sims 
<michaels at crye-leike.com> wrote:

> If they do, I test each A record, returning true if any one of the
> records is "bogus", false otherwise.

Does it make sense to reject if any host is bogus, or only if all are? I 
can imagine the case where one has deliberately seeded one's MX records 
with a bogus host (say, as the last MX entry) to catch naive spamware.

There are also misconfigured sites that list their internal mail server in 
their external MX records as the first host, with the intention that 
internal hosts will deliver to the internal server and their gateway host 
will forward to it, while external hosts will find the internal server 
inaccessible and deliver to the gateway host (listed second). (This is a 
bad configuration because a peer with the same internal network structure 
could have an internal mail server with the same address as the target 
domain's internal server, and the mail would never get to the target 
gateway.)