5.7.57 Microsoft bounce: anonymous send blocked

What 5.7.57 means

An application or device relaying through the Microsoft 365 SMTP endpoint did not authenticate, so it was rejected.

Message text

Client was not authenticated to send anonymous mail during MAIL FROM

Common causes of 5.7.57

• Application or device is not configured with SMTP authentication for smtp.office365.com

How to fix 5.7.57

1. Configure SMTP authentication in the application or device.
2. Run SPF checker and DKIM checker on the sending domain.

Check your domain

Check the SPF record of your sending domainRuns in your browser; nothing is uploaded.

Have the full bounce message? Paste it into the bounce code lookup and it will match the code and the provider for you. Open the bounce code lookup.

How to read 5.7.57

The second part, 5.7.57, is an enhanced status code (RFC 3463 §2) written class.subject.detail. Class 5 is a Permanent failure (5xx): the command was rejected and the sender should not repeat it unchanged (RFC 5321 §4.2.1; RFC 3463 §2).. Subject 7 is security or policy: authentication, authorization or policy refused the message. The detail number refines the subject, and providers may define details of their own, which is why one code can read differently at Gmail, Microsoft and Yahoo.

Do not keep resending the same message: a permanent failure repeats until the cause is fixed. Correct the cause, then send a new message.

Official source: learn.microsoft.com. Last verified 2026-10-20.

Related guides

• How to create an SPF record (syntax and examples)
• How DKIM works and how to publish a DKIM record
• How to set up a DMARC record, from p=none to p=reject

Related codes

• 5.7.0 SMTP: security status
• 5.7.1 SMTP: delivery not authorized
• 5.7.23 SMTP: SPF validation failed
• 5.7.25 SMTP: reverse DNS failed
• 5.7.26 SMTP: authentication failed
• 5.7.27 SMTP: sender has null MX

FAQ

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