Gmail 550 5.7.30: message didn't pass DKIM authentication

What the bounce means and the exact steps to stop it.

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

Other bounce errors

• Gmail 550 5.7.26
• Gmail 421 4.7.26
• Gmail 550 5.7.27 / 421 4.7.27
• Gmail 550 5.7.32 / 421 4.7.32
• Gmail 550 5.7.40 / 421 4.7.40
• Gmail 550 5.7.24 / 421 4.7.24
• Gmail 550 5.7.25 / 421 4.7.23
• Gmail 550 5.7.29 / 421 4.7.29
• Outlook / Hotmail 550 5.7.515