MailFixIt

Microsoft 365 SMTP submission error

Outlook 5.7.57: Client was not authenticated to send anonymous mail during MAIL FROM

An application or device tried to use a Microsoft 365 sending route without the authentication or connector configuration that route requires.

Problem description

The Microsoft response contains:

5.7.57 SMTP; Client was not authenticated to send anonymous mail during MAIL FROM
Is this temporary or permanent?

The enhanced status is permanent until the client uses a valid authenticated or connector-based route. The leading SMTP code can vary by context.

Configure the intended send method

  1. Identify the application or device and the Microsoft 365 endpoint it uses.
  2. Ask the tenant administrator which supported send method it should use.
  3. Match the endpoint, port, TLS, identity, and authentication settings to that method.
  4. Confirm that the mailbox and tenant allow the selected method, or that the connector matches the sending source.
  5. Send a small test and inspect Microsoft message trace.

Do not expose credentials in logs or public tools. Do not enable broad anonymous relay to make the error disappear.

Frequently asked questions

Will changing SPF fix Microsoft 365 5.7.57?

No. This response concerns SMTP client authentication or relay configuration, not public sender authorization.

Should I enter Microsoft 365 credentials in a DNS checker?

No. Store credentials only in the trusted application or device and use the method approved by your Microsoft 365 administrator.

Related email diagnostics

Outlook 550 5.7.64: TenantAttribution; Relay Access DeniedFix Microsoft 365 550 5.7.64 by reviewing the inbound connector after an on-premises mail environment change. Outlook 550 5.4.1: Relay Access DeniedDiagnose Microsoft 365 550 5.4.1 relay access denied or recipient address rejected without assuming one DNS cause. Outlook 550 5.7.515: Access denied, sending domain does not meet the required authentication levelDiagnose Outlook 550 5.7.515 email rejection safely. Check SPF, DKIM and DMARC DNS, interpret the receiver report, and identify the next configuration step.

Primary sources: Microsoft Exchange Online NDR reference, Microsoft 365 options for sending email from devices and applications.