Mail delivery failed - and then suceeded.

[#1]

Just for my enlightenment - I sent an email to a friend, and got the response below:

Delivery to the following recipients failed permanently:

   * XXX.plus.com

Reason: A message that you sent to the following recipient could not be delivered due to a permanent error. ** The remote server ?? responded with: ** XXX.plus.com ??:?? This message was created automatically by mail delivery software on the server .

Reporting-MTA: dns; avasout-peh-001 [212.159.14.17]
Received-From-MTA: dns; [192.168.178.32] [82.71.60.16]
Arrival-Date: Mon, 14 Nov 2022 16:08:08 +0000


Final-recipient: rfc822; XXX.plus.com
Diagnostic-Code: smtp; 500 command unrecognizedI

I then sent it again, and it went. That somewhat calls into question the 'permanent error' message

[#2]

These errors happen from time to time. I have not yet discerned a pattern … may be we might use this tread to profile the issue. Would be interesting to see if there’s any commonality in the error messages.

Remember that relay.plus.net is not a single server /service instance. It’s a farm of servers. There is no assurance that two different send attempts hit the same service / server instance.

[#3]

Cheers @Townman I must admit it is the first time I have seen this, although there were actually a total of three attempts to send - the first one did not give rise to a failure notice as I only discovered the message hadn't reached the recipient during a conversation yesterday - three weeks after the first attempt.

Yep, I know there is more than one mail server. 😉

[#4]

Hi John,

You might indeed know that the "server" is actually multiple service instances, but many will not.  I try to write answers which might be of general help, not always specific to the OP.  In this case, such consideration might explain a failure followed by a success.

I have a remote monitor (probe software) running on a friend's machine; each time it starts up (or something goes wrong) I get a barrage of email notices, configured to come from me, sent to me.  From time to time, I received a not delivered report from just one in the bundle of sent messages.

Not had the time nor inclination to look deeper.  Now you have raised the matter, I will add my events here - will be interesting to see if it is all the same avasout server.

[#5]

Fair enough @Townman .