Fix email delivery issues for error code 5.7.57 in Exchange Online

It's frustrating when you get an error after sending an email message. This topic 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).

Email user icon I got this bounce message. How do fix it? Email admin icon I'm an email admin. How do I fix this?

Why did I get this bounce message?

When you connect to the smtp.office365.com endpoint to submit (relay) messages through 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?

I'm an email admin. How do I fix this?

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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See also

Email non-delivery reports in Exchange Online