Enhanced SMTP status code · RFC 3463 · IANA

5.7.40 Your message was blocked because the sending domain doesn't have a DMARC record or the DMARC record doesn't specify a DMARC policy

The sending domain has no DMARC record, or it has no policy (p=); Gmail requires one from bulk senders.

Class: Permanent failure
Class 5: a permanent failure. Resending the same message will not help: something about the message, the sender or the destination must change (RFC 3463 §3.1).

Also seen as: 4.7.40
Subject: X.7 · Security and policy
Policies (per-host or per-recipient filters) and cryptographic operations; up to the sender, the recipient or both.

How 5.7.40 appears at providers

The exact text from the provider's documentation, as you see it in the bounce, and what it means.

550 5.7.40Your message was blocked because the sending domain doesn't have a DMARC record or the DMARC record doesn't specify a DMARC policy. Gmail requires all bulk email senders to add a DMARC record to their sending domain.

The sending domain has no DMARC record, or it has no policy (p=); Gmail requires one from bulk senders. Check with DMARC generator.
504 5.7.40Unrecognized authentication type.

The authentication mechanism used is not recognised.
504 5.7.40XOAUTH is no longer supported.

The XOAUTH mechanism is no longer supported; use OAuth 2.0.
421 4.7.40Your email has been rate limited because the sending domain doesn't have a DMARC record, or the DMARC record doesn't specify a DMARC policy. Gmail requires all bulk email senders to add a DMARC record to their sending domain.

The sending domain has no DMARC record, or it has no policy (p=); Gmail requires one from bulk senders. Check with DMARC generator.

Sources: RFC 5321 · RFC 3463 · RFC 3464 · IANA · Gmail · Microsoft 365 · read on 26 September 2026