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Around 30% of the emails I send get returned. If I resend, it always works.

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Around 30% of the emails I send get returned. If I resend, it always works. I am using Thunderbird 102.10.1 (64-bit) on OpenSuse Leap 15.4 The returned message is eg.

     This is an automatically generated Delivery Status Notification.      

Delivery to the following recipients failed permanently:

  * rachel.a.drysdale@gmail.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: ** rachel.a.drysdale@gmail.com ??:?? This message was created automatically by mail delivery software on the server .


Reporting-MTA: dns; avasout-ptp-003 [84.93.230.244] Received-From-MTA: dns; [192.168.0.30] [212.159.97.201] Arrival-Date: Fri, 05 May 2023 11:11:17 +0100


Final-recipient: rfc822; rachel.a.drysdale@gmail.com Diagnostic-Code: smtp; 550-5.7.26 This mail is unauthenticated, which poses a security risk to the

Last-attempt-Date: Fri, 05 May 2023 11:11:17 +0100

I compared the source for the failed message and that for the successfully re-sent message. The significant difference seems to be that order of items in the header changed: FAILED: Subject To Ref Content-Language From

SUCCEEDED: From Subject To Ref Content-Language


Does anyone have an idea about this?

Around 30% of the emails I send get returned. If I resend, it always works. I am using Thunderbird 102.10.1 (64-bit) on OpenSuse Leap 15.4 The returned message is eg. ****************** This is an automatically generated Delivery Status Notification. Delivery to the following recipients failed permanently: * rachel.a.drysdale@gmail.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: ** rachel.a.drysdale@gmail.com ??:?? This message was created automatically by mail delivery software on the server . Reporting-MTA: dns; avasout-ptp-003 [84.93.230.244] Received-From-MTA: dns; [192.168.0.30] [212.159.97.201] Arrival-Date: Fri, 05 May 2023 11:11:17 +0100 Final-recipient: rfc822; rachel.a.drysdale@gmail.com Diagnostic-Code: smtp; 550-5.7.26 This mail is unauthenticated, which poses a security risk to the Last-attempt-Date: Fri, 05 May 2023 11:11:17 +0100 ****************** I compared the source for the failed message and that for the successfully re-sent message. The significant difference seems to be that order of items in the header changed: FAILED: Subject To Ref Content-Language From SUCCEEDED: From Subject To Ref Content-Language Does anyone have an idea about this?

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Final-recipient: rfc822; rachel.a.drysdale@gmail.com

Diagnostic-Code: smtp; 550-5.7.26 This mail is unauthenticated, which poses a security risk to the

Risk to the What exactly. I think you missed a bit there. However google indicates that the 550-5.7.26 may well indicate server issues with plus net. Have you contacted them?