550 5.7.28: Unusual rate of unsolicited mail
Gmail returns 4.7.28 when it sees an unusual rate of unsolicited mail from your IP, netblock, DKIM domain, SPF domain or a URL domain in your messages, and 5.7.28 when it blocks that IP. It is a volume-and-complaints signal, not a DNS error: slow down and fix what recipients are reporting.
The exact messages
Gmail / Google Workspace
550 5.7.28 There is an unusual rate of unsolicited email originating from your IP address has been blocked.
Gmail / Google Workspace
421 4.7.28 Gmail has detected an unusual rate of unsolicited email originating from your DKIM domain.
Gmail / Google Workspace
421 4.7.28 Gmail has detected an unusual rate of unsolicited email originating from your SPF domain.
Gmail / Google Workspace
421 4.7.28 Gmail has detected an unusual rate of unsolicited email containing one of your URL domains.
Gmail / Google Workspace
421 4.7.28 Gmail has detected an unusual rate of unsolicited email originating from your IP Netblock.
Gmail / Google Workspace
421 4.7.28 Gmail has detected this sender exceeded the quota for sending messages that have the same Message-ID:.
Why it happens
- A sudden jump in volume from a domain or mailbox with little sending history.
- Recipients marking the mail as spam.
- A link domain in your messages (a shared tracking domain or URL shortener) with poor reputation.
- The same message sent many times with an identical Message-ID.
How to fix it
- Cut volume immediately and ramp back up gradually once deferrals stop.
- Check Google Postmaster Tools for spam rate and domain reputation.
- Use your own custom tracking domain rather than a shared one, or turn link tracking off.
- Remove recipients who never engage and anyone who complained.
If you send cold email
This is the classic "new domain, full volume on day one" bounce. New mailboxes need a gradual ramp, a small daily cap per mailbox, and lists that are verified before sending.
How WarmHawk handles it
WarmHawk pauses a mailbox on its own once its hard-bounce rate passes 5% over at least 20 sends, and pauses a campaign at that campaign’s own bounce threshold, so a bad list stops before it drags the domain down. Every sending domain is re-checked against DNS blocklists hourly, and a mailbox only reaches campaign volume after at least 14 days of warmup with a 90% inbox rate. A mailbox whose inbox rate falls below 70% goes back to warmup. How WarmHawk works →
Check your domain now
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Related bounce codes
- 4.7.0Temporarily deferred: low reputation, PTR or TLS
- 5.7.1Delivery not authorized, message refused
- 4.2.1Recipient is receiving mail too quickly
Sources, checked 2026-09-29: Google Workspace: Gmail SMTP errors and codes · Google: Email sender guidelines. Have a different bounce? Paste it into the decoder →
Questions
5.7.28 questions
What does 5.7.28 mean?+
Gmail returns 4.7.28 when it sees an unusual rate of unsolicited mail from your IP, netblock, DKIM domain, SPF domain or a URL domain in your messages, and 5.7.28 when it blocks that IP. It is a volume-and-complaints signal, not a DNS error: slow down and fix what recipients are reporting.
Is 5.7.28 a temporary or permanent error?+
Both forms exist. A reply starting with 4 (such as 4.7.28) is temporary, and the sending server will retry; a reply starting with 5 is permanent, and the message will not be retried until you fix the cause.
How do I fix 5.7.28?+
Cut volume immediately and ramp back up gradually once deferrals stop. Check Google Postmaster Tools for spam rate and domain reputation. Use your own custom tracking domain rather than a shared one, or turn link tracking off. Remove recipients who never engage and anyone who complained.