550 5.7.1 — message rejected by policy

A generic policy rejection. The accompanying text says which policy fired — most often DMARC, SPF, or a recipient-side rule.

What causes it

• The recipient domain publishes p=reject and your message failed DMARC.
• Your own domain published -all and the sending IP was not listed.
• An organisational rule at the receiver unrelated to authentication.

How to fix it

Read the full text after the code — "SPF check failed", "DMARC policy" and "blocked by administrator" call for entirely different fixes. If it names DMARC, run the domain through the checker below and look at alignment first.

Check your domain

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