John L wrote:
If that's the case, shouldn't the deprecating of A lookups when a MX
lookup fails be brought to the SMTP group?
I'm sure this has come up before, but it's probably worth running by
them again. This was intended to be a transitional feature 25 years
ago, and given how few legit MTAs are identified by A records, we should
try to declare the transition to be over.
Good luck!!!
It has nothing to do with many "few legit" exists (which is more than
you think), but how many legacy and current SMTP systems exist that
would have to be updated!! Expecting burned in stone working history
of all the many smtp servers out there, with continued clear cut
operational issues with sysops, to alter their system for this is asking
a bit much.
A reminder from the 2821 standard:
5. Address Resolution and Mail Handling
....... The lookup first attempts to locate an MX
record associated with the name. If a CNAME record is found instead,
the resulting name is processed as if it were the initial name. If
no MX records are found, but an A RR is found, the A RR is treated as
if it was associated with an implicit MX RR, with a preference of 0,
pointing to that host. If one or more MX RRs are found for a given
name, SMTP systems MUST NOT utilize any A RRs associated with that
name unless they are located using the MX RRs; the "implicit MX" rule
above applies only if there are no MX records present. If MX records
are present, but none of them are usable, this situation MUST be
reported as an error.
That said, some systems, such as our own, have a one attempt only for
the "Implicit MX" rule. i.e. No MX -> A Lookup --> 1 attempt only.
This past week alone we would have electronic mail communications fails
with legit customers lacking MX records if this rule was enforced.
I just can't see this happening. I will have to see snow balls falls
from these South Florida skies before I would have our SMTP system
changed.
--
Hector Santos, CTO
http://www.santronics.com
http://santronics.blogspot.com
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