Re: DNS question, null MX records

[Tony Finch <dot () dotat at>]

On Wed, 16 Dec 2009, Douglas Otis wrote:
> To avoid server access and hitting roots:
>
> host-1.example.com. IN A 192.0.2.0
> host-10.example.com. IN A 192.0.2.9
>
> example.com.  IN MX 0 host-1.example.com.
> example.com.  IN MX 90 host-10.example.com.

This is not very good from the point of view of a legitimate but mistaken
sender, because their messages will be queued and retried. The advantage
of pointing MX records at nonexistent hosts is most MTAs (and all common
ones) will stop trying to deliver the message immediately. It is perhaps
more polite to use a nonexistent name that you control, but that doesn't
allow the source MTA to skip further DNS lookups, unlike the nullmx or
sink.arpa ideas.

Tony.
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