> - if we fail on an MX lookup should we defer immediately or
> continue trying a DNS lookup for A record.
No.
> The purist in me say's this is not a good thing to do, but the pragmatist
> says it's obvious from the above example that in some cases we will get
> a timeout doing an MX lookup when we can get a valid response for an
> A record. :-(
Indeed, it is possible if the host is a NS for its own domain, as this
requires
glue A RRs in the parent zone :-((
However, I'd suggest *not* using such A RRs, as the zone is b*ggered !
[[ yes, I may use them when sending email to the zone manager saying "your zone
is broken", but that is another matter ]]
> Checking an A record after MX soft failure seems to be an easy change.
... but will achieve the *WRONG* effect !
Email will be sent to the *wrong* machine.
