On Sun, Aug 24, 2025 at 07:39:17PM +0100, Simplelists - Andy Beverley via
mailop wrote:
> > delivery102.simplelists.com. IN A 91.234.234.172
>
> I've just checked now and interestingly the deliveries to the same Gmail
> server immediately before and immediately after succeeded. If it had been an
> actual DNS error I would have expected more than one failure because of
> caching (although who knows what's the other side of that single IP
> address):
Does the system in question have just one source IP address? Or is
possible that some deliveries appear to the receiving systems to
originate from different IPs than do others?
> 2025-08-19T15:00:26.602590+00:00 ...
> relay=gmail-smtp-in.l.google.com[142.251.16.27]:25, delay=3.5,
> delays=0.1/0.42/0.6/2.4, dsn=2.0.0, status=sent (250 2.0.0 OK ... - gsmtp)
>
> 2025-08-19T15:00:26.668032+00:00 ...
> relay=gmail-smtp-in.l.google.com[142.251.16.27]:25, delay=2.8,
> delays=0.11/1.2/0.62/0.82, dsn=5.7.25, status=bounced (host
> gmail-smtp-in.l.google.com[142.251.16.27] said: 550-5.7.25 [91.234.234.172]
> The IP address sending this message does not have a 550-5.7.25 PTR record
>
> 2025-08-19T15:00:26.973530+00:00 ...
> relay=gmail-smtp-in.l.google.com[142.251.16.27]:25, delay=3.2,
> delays=0.1/1.1/0.67/1.3, dsn=2.0.0, status=sent (250 2.0.0 OK ... - gsmtp)
If the IP address is sure to have been the same, and *all* your
nameservers had consistent zone content at that time, then perhaps
there's a bug.
> > Had the relevant DNS queries resulted in timeouts or other transient
> > lookup problems, and the remote MTA were Postfix, the reject code would
> > have been a 4XX. I don't know that Gmail gets this right, but I'd be
> > surprised if they got it wrong, that'd be a serious bug, worth
> > contacting their engineering team about.
>
> Anyone have a contact...?
I do have a contact on the Google mail team, but first let's be sure to
rule out any issues on your end. I'd like to recommend monitoring of
the correctness of the zone data by issuing regular (say every 5
minutes) queries checking the FCrDNS consistency of all your outbound
MTA source IPs at each of the nameservers IP addresses, and over all
available transports (UDP, TCP, DoT, ...).
Also, how frequently do you see this type of reject?
--
Viktor. 🇺🇦 Слава Україні!
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