On Sun, Aug 24, 2025 at 02:20:45PM +0100, Simplelists - Andy Beverley via mailop wrote:
> > If failure to resolve SPF, DKIM, or DMARC related DNS records leads the > > receiving MTA to issue a 5XX hard error, rather than a 4XX tempfail, the > > receiving MTA (or its content inspection stack) is badly busted. As a > > community with domain expertise, we need to make a fuss until any such > > MTAs are fixed. > > This is an example of the Gmail bounce we (very intermittently) see: > > relay=gmail-smtp-in.l.google.com[142.251.16.27]:25, delay=2.9, > delays=0.1/0.21/0.63/2, 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 setup, or the corresponding forward DNS entry does not > 550-5.7.25 match the sending IP. As a policy, Gmail does not accept messages > 550-5.7.25 from IPs with missing PTR records. For more information, go to > 550-5.7.25 https://support.google.com/a?p=sender-guidelines-ip > 550-5.7.25 To learn more about Gmail requirements for bulk senders, visit > 550 5.7.25 https://support.google.com/a?p=sender-guidelines. - gsmtp > (in reply to end of DATA command)) This appears to suggest that Gmail's MTA encountered either NXDOMAIN for the PTR query, which is not the case currently: 172.234.234.91.in-addr.arpa. IN PTR delivery102.simplelists.com. or else the returned name unequivocally (different result or NXDOMAIN, not SERVFAIL, ...) did not forward map to the same name, which is also not the case currently: delivery102.simplelists.com. IN A 91.234.234.172 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. -- Viktor. 🇺🇦 Слава Україні! _______________________________________________ mailop mailing list mailop@mailop.org https://list.mailop.org/listinfo/mailop
