421 4.7.26 Gmail bounce: unauthenticated rate limit
What 421 4.7.26 means
Gmail is slowing mail from a sender whose messages fail SPF and DKIM, so the message is deferred.
Message text
This email has been rate limited because it is unauthenticated…
This is an excerpt: the provider's documentation shortens the message. Full text: provider documentation
Common causes of 421 4.7.26
- Neither SPF nor DKIM passes for the sending domain
- Sending service not authorised in the SPF record
How to fix 421 4.7.26
- Run SPF checker and add the sending service to the record.
- Set up DKIM signing and confirm it with DKIM checker.
- Run DMARC checker to see whether the domain needs an aligned pass.
Check your domain
Check the SPF record of your sending domainRuns in your browser; nothing is uploaded.
Get your domain's deliverability score
Have the full bounce message? Paste it into the bounce code lookup and it will match the code and the provider for you. Open the bounce code lookup.
How to read 421 4.7.26
The first part, 421, is the SMTP reply code. Service not available, closing transmission channel: the server is shutting down or refusing the connection for now. Replies that start with 4 are temporary and replies that start with 5 are permanent (RFC 5321 §4.2.1).
The second part, 4.7.26, is an enhanced status code (RFC 3463 §2) written class.subject.detail. Class 4 is a Persistent transient failure (4xx): the command was not accepted, but the condition may clear, so the sender should try again later (RFC 5321 §4.2.1; RFC 3463 §2).. Subject 7 is security or policy: authentication, authorization or policy refused the message. The detail number refines the subject, and providers may define details of their own, which is why one code can read differently at Gmail, Microsoft and Yahoo.
Sending servers should retry a deferred message. RFC 5321 §4.5.4.1 advises waiting at least 30 minutes between attempts and trying for at least 4 to 5 days before giving up and returning a bounce. If the deferral keeps repeating, fix the cause rather than waiting.
Official source: knowledge.workspace.google.com. Last verified 2026-10-20.
Related guides
- How to create an SPF record (syntax and examples)
- How DKIM works and how to publish a DKIM record
- How to set up a DMARC record, from p=none to p=reject
Related codes
- 4.7.26 Microsoft: ipv6 needs spf or dkim
- 451 4.7.26 Gmail: dmarc lookup failed
- 4.7.0 SMTP: security status
- 421 4.7.0 Gmail: no PTR record
- 451 4.7.23 Gmail: PTR record missing
- 421 4.7.28 Gmail: rate limited
FAQ
What does 421 4.7.26 mean?
Gmail is slowing mail from a sender whose messages fail SPF and DKIM, so the message is deferred. This is a temporary failure.
How do I fix 421 4.7.26?
Run SPF checker and add the sending service to the record. Set up DKIM signing and confirm it with DKIM checker. Run DMARC checker to see whether the domain needs an aligned pass.
Is 421 4.7.26 permanent, and should I retry?
421 4.7.26 is a temporary failure. Your mail server normally retries by itself; if it keeps repeating, fix the cause.