Gmail 550 5.7.30: message didn't pass DKIM authentication

Short answer: The message had no valid DKIM signature for your domain. Fix: enable DKIM in the sending service, publish its key exactly as given, and make sure nothing changes the message after it is signed.

The bounce looks like this
550-5.7.30 This message was blocked because it didn't pass DKIM authentication.
421-4.7.30 Your email has been rate limited because DKIM authentication didn't pass for this message.

What it means

The message had no valid DKIM signature for your domain: DKIM is not enabled in the sending service, the public key was never published (or was copied with a typo), or the message was changed after signing (for example by a forwarder or footer tool).

How to fix it

  1. Run the checker – it looks for DKIM keys on 40+ common selectors and flags weak 1024-bit keys.
  2. In the sending service, open its domain authentication / DKIM page and publish exactly the records it shows (CNAME or TXT, host name included).
  3. Click “verify” or “start authentication” in that service – many (Google Workspace, Microsoft 365) do not sign until you do.
  4. Send a test to a Gmail address, open “Show original” and confirm DKIM: PASS with your domain.

Check your domain now

Rather not touch DNS? I set up SPF, DKIM and DMARC without breaking your other senders, with a before/after report.

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Prefer to do it yourself? Get the step-by-step Fix Kit ($15) – 19-page guide, checklist, 20+ providers.

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