[Mimedefang] DNS and MX records

[WBrown at e1b.org]

mimedefang-bounces at lists.roaringpenguin.com wrote on 05/10/2006 08:57:53 
AM:

> That is known as the implicit MX and is held over from before the MX
> resource record existed.  However, in my opinion, it has long outlived
> it's usefulness and now poses issues when a domain really doesn't want
> to have mail exchanged in their name.  I've resorted to using an MX
> record of "0 ." for my domains that do not send or receive mail.  This
> at least causes an immediate bounce and saves mail servers from 
connecting
> to a web server for 5 days.

I've taken several approaches to blocking mail.  On some domains, I set up 
an MX record that points to a server where the access file rejects 
everything for the domain.  I usually do this where the domain used to 
accept mail and real humans may still try sending to it.

The other thing is to put the server the A record points to behind a 
firewall that drops all traffic except that which is expected.  Usually, 
domain.tld would be the same as www.domain.tld, registered for those too 
lazy to type "www."
as part of the address.  Of course marketing type like to say "Visit us 
online at sony.com!!"

The later ties up the sending host a little because it has to wait for the 
packet to time out because of the drop rule.  And who cares if they keep 
trying for 5 days.