[Mimedefang] Validating sender domain opinion

[WBrown at e1b.org]

mimedefang-bounces at lists.roaringpenguin.com wrote on 07/08/2004 09:37:16 
AM:

> What about a DNS configuration with an invalid private MX as first one?

They are probably lazy and do not have split DNS servers, or seperate ones 
for internal vs external resolution.  The external ones are filters, and 
the one with the private network address is the actual mail server.
 
> ;; ANSWER SECTION:
> mox.de.                 252     IN      MX      30 mail.portunity.de.
> mox.de.                 252     IN      MX      10 192.168.100.251.
> mox.de.                 252     IN      MX      20 mail.mox.de.
> 
> These are not spammers, BTW.
> 
> I would consider such setup invalid and my code had rejected the mail, 
if 
> it were enable. -- I mean, why does they try to deliver mail to one of 
my 
> hosts, private addresses are "my hosts", aren't they?
> I ignore the fact here intentionally, that they do point to a numerical 
> address rather than a symbolic host.

Actually, it is invalid.  MX records should not have numeric values for 
the host, rather a "domain-name which specifies a host willing to act as a 
mail exchange for the owner name."  (per DNS and BIND, P. Albitz & C. Liu, 
page 533)

If you want to block it, you could, but would your users like that?  Do 
you feel like teaching the mail admin at mox.de how to fix their mail 
and/or DNS system?

> What do you think?