[Mimedefang] DNS and MX records

[John Rudd]

On May 10, 2006, at 5:57 AM, Jason Bertoch wrote:

>
>
>> If I'm not mistaken, even properly configured MTAs will revert to the 
>> A
>> record of a domain of there are no MX records available. (although I
>> haven't done any real research to back up this statement recently so I
>> could be completely off base)
>>
>> Alan
>
> 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.
>

Uh, I think the way you're supposed to solve that problem (a domain 
that doesn't receive email) is by:

a) not having an MX record,
b) not having the hosts answer on port 25, or if they're shared among 
multiple domains, have them refuse email directed at recipients of that 
domain.

(and, do correct me if I'm wrong: I thought MX records were optional; 
you use them when you want email sent to some place OTHER than the 
matching hostname; if you want email to go directly to a host, it's ok 
to not have an MX record for that host)

And, the way I handle not having anyone connect to port 25 on my web 
server is ... my web server doesn't run any software on port 25.  If 
people are trying to send it email directly, and that email gets stuck 
in their mail queue for 5 days because of it, that's their problem, not 
mine.