421 4.7.26: unauthenticated mail, rate limited
Gmail is slowing mail from you because this message passed neither SPF nor DKIM, and Gmail requires every sender to pass at least one.
- Gmail
- Provider
- Temporary (4xx)
- Class
- Sources checked
- Author
At a glance
- Code
- 421 4.7.26
- Provider
- Gmail and Google Workspace
- Temporary or permanent
- TemporaryThe sending server keeps the message and tries again later.
- Who has to act
- The sender. The fix is on the sending side: your domain, your server or your list.
- What the server says
421 4.7.26 This email has been rate limited because it is unauthenticated.
What it means
Since February 2024 Google's sender guidelines have required everyone who sends to Gmail to authenticate with SPF or DKIM. This message passed neither, so Gmail has rate limited it. The reply lists the results Gmail saw: DKIM did not pass, and SPF for the envelope domain and the sending IP did not pass. This is the temporary form; the permanent one is 550 5.7.26. Typical reasons are a new sending service that was never added to SPF, DKIM signing that was never switched on, or forwarding that breaks SPF with no DKIM signature to fall back on.
Common causes
- The sending server or service is not listed in the envelope domain's SPF record.
- DKIM signing is not turned on for the domain, or the selector record is missing from DNS.
- Forwarding or a relay changed the path, so SPF fails and no valid DKIM signature survives.
How to fix it
- 01Read the authentication results in the bounce to see which domain and IP Gmail checked.
- 02Add every service that sends for you to your SPF record.
- 03Turn on DKIM signing at each sending service and publish its selector record.
- 04Send a test to a Gmail address and confirm that SPF or DKIM shows pass in its headers.
Sources
What this page rests on, checked on 20 Oct 2026. The explanation is ours; the reply text is the server's.
- Gmail SMTP errors and codes (Google Workspace Admin Help)knowledge.workspace.google.com
- Email sender guidelines (Gmail Help)support.google.com
Related codes
- 550 5.7.26Unauthenticated sender, blocked.Gmail rejected the message because it passed neither SPF nor DKIM, and Gmail requires every sender to pass at least one.
- 421Service not available.The receiving server is closing the connection and will not take mail right now. The reply is temporary, so the sending server keeps the message and tries again later.
- 550 5.7.26Multiple authentication checks failed.The message failed more than one authentication check, for example SPF and DKIM, and the receiving server's policy rejects it.
4.7.26 at other providers
Further reading
All 108 Gmail codesEvery code in the wikiPaste your own bounce