Gmail temporary traffic/reputation error
Fix Gmail 421 4.7.28 unusual email rate limiting
Gmail uses 421 4.7.28 for temporary rate limiting tied to unusual or unsolicited email. The complete response identifies whether the signal concerns overall rate, an IP/netblock, SPF or DKIM domain, URL domain, or repeated Message-ID.
A representative response is:
421 4.7.28 Gmail has detected an unusual rate of unsolicited email.
421 is temporary. Keep backoff-based retries, reduce pressure, and investigate before restoring volume.
What to investigate
- Unexpected volume or concurrency changes.
- Compromised accounts, credentials, queues, or web forms.
- Complaint rate, invalid recipients, and weak consent evidence.
- A shared IP, sending domain, or linked domain with degraded reputation.
- Repeated Message-ID generation defects.
Resolution sequence
- Preserve the complete variant and affected identity.
- Pause suspicious campaigns and secure the sending path.
- Suppress invalid/unsubscribed recipients and verify opt-in.
- Warm legitimate traffic gradually; do not create retry storms.
- Monitor Gmail Postmaster Tools where eligible.
Frequently asked questions
Is Gmail 421 4.7.28 temporary?
Yes. The sending system should retry with backoff while the operator investigates unusual traffic or unsolicited-mail signals.
Is this an SPF error?
Not by itself. Gmail documents rate, IP, subnet, DKIM domain, SPF domain, URL domain, and unsolicited-volume variants.
Can MailFixIt remove the rate limit?
No. Gmail controls its rate and reputation decisions; this page provides operational remediation.
Related email diagnostics
Primary sources: Gmail SMTP errors and codes and Google email sender guidelines.