Why did my email messages to Gmail receive a “421 4.7.30 This mail has been rate limited because DKIM does not pass. Gmail requires all large senders to authenticate with DKIM. Authentication results: DKIM = did not pass” message?

Starting on February 1, 2024, Google has imposed new requirements on bulk senders, including a requirement to utilize DKIM or SPF, along with DMARC.

One of the new error messages that Google may return for Gmail recipients is:

421 4.7.30 This mail has been rate limited because DKIM does not pass. Gmail requires all large senders to authenticate with DKIM. Authentication results: DKIM = did not pass

This new error message is a temporary failure for senders who do not have a working DKIM record.

To resolve this and get email delivered to Gmail again, you must implement or correct DKIM for your message stream.

Additional Reading

• Google’s Email Sender Guidelines
• Google’s Email Sender Guidelines FAQ
• Gmail SMTP