This is an automatically generated Delivery Status Notification.      

  * raifenton@gmail.com

Hello, I am having trouble sending Email messages to gmail addresses. This problem only started a few weeks ago. These messages are being blocked, with a failure report being sent back to me. This particular report example is of failure when sent from my address rai@raisig.net to my own gmail address! What can be done to my Thunderbird outgoing message settings to satisfy the gmail checks, please? Rai Fenton <Message Delivery Failure report start> This is an automatically generated Delivery Status Notification. Delivery to the following recipients failed permanently: * raifenton@gmail.com Reason: There was an error while attempting to deliver your message with [Subject: "Reminder, next walk - Friday 22nd April - Wanstead Park"] to raifenton@gmail.com. MTA p3plwbeout05-02.prod.phx3.secureserver.net received this response from the destination host IP - 173.194.205.26 - 550 , 550-5.7.26 This message does not have authentication information or fails to 550-5.7.26 pass authentication checks. To best protect our users from spam, the 550-5.7.26 message has been blocked. Please visit 550-5.7.26 https://support.google.com/mail/answer/81126#authentication for more 550 5.7.26 information. h12-20020a05620a244c00b0069ad44d7f43si132489qkn.700 - gsmtp . Reporting-MTA: dns; p3plwbeout05-02.prod.phx3.secureserver.net [97.74.135.83] Received-From-MTA: dns; mailex.mailcore.me [94.136.40.141] Arrival-Date: Tue, 19 Apr 2022 09:12:38 -0700 Final-recipient: rfc822; raifenton@gmail.com Diagnostic-Code: smtp; 550-5.7.26 This message does not have authentication information or fails to Last-attempt-Date: Tue, 19 Apr 2022 09:12:39 -0700 <end of Message Delivery Failure report>