Seems that gmail.com's MTA can't properly speak SMTP. I've been seeing re-queuing and re-sending of permanent failures for some time now, but now I'm seeing its user simply hitting forward and sending the bounce to the original failed recipient.
.. I do get pretty worked up by not being able to follow the RFCs and normally just shake my head, but this is some pretty basic stuff; I give you a 5xx response -- that's a permanent failure, not a temporary one! From: Mail Delivery Subsystem <mailer-dae...@googlemail.com> Date: June 5, 2021 at 9:55:58 AM EDT To: [redacted]@gmail.com Subject: Delivery Status Notification (Delay) [redacted] Delivery incomplete There was a temporary problem delivering your message to [redacted]. Gmail will retry for 47 more hours. You'll be notified if the delivery fails permanently. The response from the remote server was: 554 [redacted] -- SgtChains _______________________________________________ mailop mailing list mailop@mailop.org https://list.mailop.org/listinfo/mailop
