When sending emails from a Microsoft 365 email account, you may sometimes receive a bounce-back email that reports that you are “not authorized to relay messages through the server that reported this error“.

office 365 email bounce error - not authorized

A log of details regarding the message may also be included in the bounce-back email, along with a Reported Error similar to the below examples;

  • “550 5.7.367 Remote server returned not permitted to relay -> 550 5.7.1 relaying denied”
  • “550 5.7.367 Remote server returned not permitted to relay -> 550 relay not permitted”
  • “550 5.7.368 Remote server returned authentication required to relay -> 550 Please turn on SMTP Authentication in your mail client. […] is not permitted to relay through this server without authentication.”

This email essentially is advising that the receiving server had an issue passing your email on to the intended recipient’s email account. This could indicate a possible issue with the receiving mail server, or that it may not be configured correctly.

Resolving the Issue

Ultimately, the issue resides with the recipient’s email server and can’t be fixed by yourself or Conetix.

Before contacting the intended recipient via a different method to let them know of the issue (eg, by using a different email address or calling them by phone), you may first wish to check the message at the very top of the bounce-back email to confirm that you are sending the email to the correct address;

“Your message to [recipient email address] couldn’t be delivered.”

If this address is incorrect or not the address you were expecting, you may simply need to re-send the email to the correct email address.

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