# 550 5.7.57: client was not authenticated to send anonymous mail

URL: https://iblockspam.com/smtp-errors/550-5-7-57
Last updated: 2026-10-09

Code: 550 5.7.57 (permanent failure, the message bounced)
Provider: Microsoft 365 / Outlook.com

An application or device tried to send through Microsoft 365's smtp.office365.com without authenticating with a valid mailbox's credentials.

What the bounce says:

```
Client was not authenticated to send anonymous mail during MAIL FROM
```
Microsoft's description for 5.7.57 in its Exchange Online NDR reference.

Microsoft explains that when you connect to the smtp.office365.com endpoint to submit (relay) messages through Microsoft 365, you need to authenticate with the credentials of a user who has an Exchange Online mailbox. A 5.7.57 bounce means there's a problem in the configuration of the connecting application or device.

Microsoft's fix has two checks: verify that the credentials in the application or device are correct, and verify that the application or device can negotiate TLS, because TLS is required in order to authenticate. Microsoft adds that the line between end user and admin is blurred for this error, because the problem lies in the device's configuration.

This typically hits scanners, printers, line-of-business apps and website contact forms. Microsoft's guide for devices says client SMTP submission needs TLS 1.2 or later. A device that can't do that won't be able to authenticate; for those, Microsoft documents other options, such as relaying through a connector.

## Common causes

- The device or app has no username and password set, or they're wrong.
- TLS is turned off, or the device can't negotiate a TLS version Microsoft 365 accepts.
- The account used has no Exchange Online mailbox.

## How to fix it (sender)

- Check the server (smtp.office365.com), port, username and password in the device's email settings.
- Turn on TLS/STARTTLS in the device; update its firmware if it can't negotiate TLS.
- Use an account that has an Exchange Online mailbox.

## How to fix it (recipient or admin)

- No action needed: the failure happens before the message leaves the sender.

**Q: Why does my scanner get 5.7.57 when the password is right?**
Microsoft requires TLS before authentication. If the scanner can't negotiate TLS, or TLS is off in its settings, sign-in fails even with the right password.

**Q: Does the sending account need a license?**
Microsoft says you must authenticate with the credentials of a user who has an Exchange Online mailbox.

Sources:
- Fix NDR error "550 5.7.57" in Exchange Online (Microsoft Learn): https://learn.microsoft.com/en-us/troubleshoot/exchange/email-delivery/ndr/fix-error-code-5-7-57-in-exchange-online
- How to set up a multifunction device or application to send email using Microsoft 365 (Microsoft Learn): https://learn.microsoft.com/en-us/exchange/mail-flow-best-practices/how-to-set-up-a-multifunction-device-or-application-to-send-email-using-microsoft-365-or-office-365
- Email nondelivery reports (NDRs) and SMTP errors in Exchange Online (Microsoft Learn): https://learn.microsoft.com/en-us/troubleshoot/exchange/email-delivery/ndr/non-delivery-reports-in-exchange-online

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