550 5.7.57: SMTP client submission without authentication
A device or application tried to send through smtp.office365.com without authenticating as a user with an Exchange Online mailbox.
- Microsoft
- Provider
- Permanent (5xx)
- Class
- Sources checked
- Author
At a glance
- Code
- 550 5.7.57
- Temporary or permanent
- PermanentRefused for good: the message comes back to the sender, and resending it gets the same answer.
- Who has to act
- The sender. The fix is on the sending side: your domain, your server or your list.
- What the server says
550 5.7.57 Client was not authenticated to send anonymous mail during MAIL FROM
What it means
SMTP client submission to smtp.office365.com requires the connecting application or device to authenticate with the credentials of a user who has an Exchange Online mailbox, and authentication needs TLS, so the device must negotiate TLS first. When it tries to send without authenticating, Exchange Online answers with 5.7.57. It is a configuration problem in the printer, scanner, script or application, so whoever manages that device fixes it; Microsoft notes that the line between user and admin is blurred for this one.
Common causes
- The device or application has no credentials configured, or wrong ones.
- It cannot negotiate TLS, so it never gets to authenticate.
- It was set up for anonymous relay but points at smtp.office365.com.
How to fix it
- 01Enter the username and password of a user with an Exchange Online mailbox in the device or application settings.
- 02Make sure the device supports TLS and uses it when connecting.
- 03If it cannot authenticate, use one of the other methods in Microsoft's guide to setting up a multifunction device or application to send email.
Sources
What this page rests on, checked on 20 Oct 2026. The explanation is ours; the reply text is the server's.
- Fix NDR error "550 5.7.57" in Exchange Onlinelearn.microsoft.com
- Email nondelivery reports and SMTP errors in Exchange Onlinelearn.microsoft.com
Related codes
Further reading
All 111 Microsoft codesEvery code in the wikiPaste your own bounce