Fix NDR error "550 5.7.57" in Exchange Online
It's frustrating when you get an error after sending an email message. This article describes what you can do if you see error code 550 5.7.57 in a non-delivery report (also known as an NDR, bounce message, delivery status notification, or DSN).
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I got this bounce message. How do I fix it? | 
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I'm an email admin. How can I fix this error? |
Why did I get this bounce message?
When you connect to the smtp.office365.com endpoint to submit (relay) messages through Microsoft 365 or Office 365, you need to authenticate with the credentials of a user who has an Exchange Online mailbox. This bounce message indicates a problem in the configuration of the connecting application or device.
I got this bounce message. How do I fix it?
In the configuration of the connecting application or device, verify that the specified credentials are correct.
Verify that the application or device is able to negotiate TLS, as TLS is required in order to authenticate. For more information, see How to set up a multifunction device or application to send email.
I'm an email admin. How do I fix this error?
The distinction between an end user and an admin is blurred for this bounce message, as the problem lies within the configuration of the application or device.
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