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Gmail 421 4.7.0 — Unusual Rate of Unsolicited Mail / Try Again Later

Gmail temporarily refused the connection. The text names one of several conditions: an unusual rate of unsolicited mail from the IP, a transient system condition, or authentication that could not be verified.

Diagnose your exact bounce Email Infrastructure Digital Twin

What the bounce says

Exact wording as it appears in the rejection or NDR. Placeholders such as x.x.x.x and example.com stand for your own address and domain.

421-4.7.0 [x.x.x.x] Our system has detected an unusual rate of unsolicited mail originating from your IP address. To protect our users from spam, mail sent from your IP address has been temporarily rate limited.

421-4.7.0 Try again later, closing connection.

421-4.7.0 This message does not have authentication information or fails to pass authentication checks (SPF or DKIM). To best protect our users from spam, the message has been blocked.

Gmail uses 421 4.7.0 for several temporary refusals and distinguishes them only by the text. One says the IP is sending unsolicited mail and has been rate limited; one says try again later; one says authentication is missing. Each has a different fix.

Reviewed 2026-09-08. Provider wording and requirements change; the provider reference below is authoritative.

Most common causes

  • The sending IP recently sent mail Gmail classified as unsolicited
  • A new IP or a sudden volume increase
  • Transient load on Gmail’s side
  • Authentication missing or failing on a path Gmail treats as temporary

What to verify next

  1. Read the text after 4.7.0 — rate limiting, "try again later" and authentication variants are different problems
  2. Retry with backoff; do not resend manually
  3. Check Postmaster Tools for IP and domain reputation
  4. Verify SPF and DKIM for the real sending path

Three messages, three causes

"Unusual rate of unsolicited mail" is a reputation throttle for the IP: recent mail from it was classified as spam. "Try again later, closing connection" is a transient condition or a connection-level throttle without a reputation verdict. "Does not have authentication information" is the temporary form of the authentication requirement — the message lacked passing SPF or DKIM.

Read the full sentence; the fixes do not overlap.

  • Unsolicited-mail variant: reputation.
  • Try-again variant: transient or connection throttle.
  • Authentication variant: SPF/DKIM missing.

Reputation throttle

Reduce volume to Gmail, review what was sent recently for anything recipients would report, check Postmaster Tools for the IP and domain reputation, and confirm PTR and authentication. The throttle lifts as the spam rate observed by Gmail falls.

Authentication variant

Configure SPF and DKIM for the real sending path and verify with a test message. Gmail retries a few times; if authentication is not fixed the message eventually bounces with 5.7.26.

Best diagnostic path

Live analysis

Mail Failure Doctor

Classify the complete rejection and preserve provider-specific diagnostic context.

Open analysis → Live analysis

Email Infrastructure Digital Twin

Map the domain’s public mail infrastructure and provider relationships before remediation.

Open analysis →

Known limits

  • Gmail does not expose the exact spam rate that triggered a throttle.
  • Postmaster Tools requires verified domain ownership.

Common questions

Should I retry immediately?

No. Let the queue back off. Retrying faster extends the throttle.

Is 4.7.0 the same as 4.7.28?

4.7.28 is specifically an unusual sending rate for an identity. 4.7.0 covers reputation, transient and authentication variants.

How long does a reputation throttle last?

Hours to a day, depending on how much the observed spam rate drops.

Why the exact message matters

The same status family can be triggered by different conditions, and providers frequently add diagnostic text that narrows the issue. Use the complete rejection text rather than treating the numeric code as a complete diagnosis.

Provider reference

For the provider-defined meaning and current requirements, review Gmail SMTP errors and codes.