On 2023-07-12 at 18:38:05 UTC-0400 (Wed, 12 Jul 2023 15:38:05 -0700)
Robert L Mathews via mailop <[email protected]>
is rumored to have said:
Today I had a customer complain that mail they send to AOL or Yahoo
addresses was being returned with:
451 Message temporarily deferred due to unresolvable RFC.5321 from
domain; see https://postmaster.yahooinc.com/error-codes
According to that page,
"- These errors indicate that the domain used to the right of the @ in
the MAIL FROM does not appear to be a real domain.
- We determine if the domain name exists by using an SOA query;
therefore, if multiple subdomains are used in MAIL FROM commands, then
besides setting up a DNS A or MX record (perhaps using a wildcard),
then SOA records must be set up as well."
This is surprising!
It's also not the whole story.
Yahoo does not reject mail from valid addresses in subdomains of
scconsult.com which have MX or A records but no SOA or NS records.
I have done absolutely nothing to achieve that. I only know it to be
true because someone mentioned this issue on some mailing list a few
weeks ago and I tested myself.
Supposedly, Yahoo is basing this on the PSL, only requiring domains at
registry boundaries to have SOAs. This much more subtle than but just as
stupid as what their error page says.
It's not at all logically hard to meet that arbitrary requirement, you
just need a zone cut everywhere you have a MX record. I've run a DNS and
mail hosting environment that way. Zone files are very small and
numerous. *Logistically* changing an existing zone with many MXs for
subdomains to that model could be a serious chore.
--
Bill Cole
[email protected] or [email protected]
(AKA @grumpybozo and many *@billmail.scconsult.com addresses)
Not Currently Available For Hire
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