550 5.7.28: unusual rate of unsolicited email from your IP
Gmail blocked mail from your IP address because it saw an unusual rate of unsolicited email coming from it. Unlike 421 4.7.28, this is a permanent rejection.
550 5.7.28 There is an unusual rate of unsolicited email originating from your IP address. To protect our users from spam, email sent from your IP address has been blocked.
The 5.7.28 message in Google's Gmail SMTP errors and codes reference, without its closing link to the sender guidelines.
What 550 5.7.28 means
Google lists 550 5.7.28 for an unusual rate of unsolicited email from your IP address, with email from that IP blocked. It's the permanent counterpart of the 421 4.7.28 replies, where Gmail rate limits mail from an IP, netblock, DKIM domain, SPF domain or URL domain after detecting an unusual rate of mail.
Gmail's sender guidelines tie this to how recipients react. Google asks senders to keep spam rates reported in Postmaster Tools below 0.10% and to avoid ever reaching 0.30% or higher, to send only to people who opted in, and to make unsubscribing easy. A sudden volume increase from a new or cold IP also looks like spam.
Common sources: a compromised mailbox, website form or script sending spam; a purchased or old list; or a shared IP where another sender's mail affects you. Find and stop the source first. Then send only wanted mail at steady volumes so the IP's reputation can recover, and use Google Postmaster Tools to watch spam rate and reputation.
Likely causes
- A compromised account, website form or script sending spam from your IP.
- Mail to purchased, scraped or stale lists that recipients report as spam.
- A sudden spike in volume from a new or rarely used IP.
- A shared IP used by other senders with poor practices.
How to fix it
If you sent the message
- Find and stop any unwanted mail from the IP: check mail queues, accounts and web forms.
- Send only to recipients who opted in, and remove addresses that bounce or complain.
- Support one-click unsubscribe for marketing mail and keep volume steady.
- Monitor spam rate and reputation in Google Postmaster Tools.
If you're the recipient or their admin
- No action needed at Gmail: the sender has to fix their sending practices.
Frequently asked questions
How is 550 5.7.28 different from 421 4.7.28?
421 4.7.28 is a temporary rate limit: your server retries later. 550 5.7.28 is a block: the message bounces. Both come from Gmail detecting an unusual rate of unsolicited mail, so the fix is the same.
What spam rate should I stay under to avoid Gmail blocks?
Google asks senders to keep the spam rate reported in Postmaster Tools below 0.10% and to avoid ever reaching 0.30% or higher.
Sources
Provider messages are quoted as the provider publishes them. Servers can change their wording, so the bounce you received may differ slightly.
Related codes
- 421 4.7.28 421 4.7.28: Gmail has detected an unusual rate of email
- 550 5.7.1 550 5.7.1: Gmail blocked likely unsolicited mail or low reputation
- 421 4.7.0 421 4.7.0: Gmail is temporarily deferring your mail
- 550 5.7.24 550 5.7.24: the sending domain's SPF record has suspicious entries
- 550 5.7.40 550 5.7.40: Gmail blocked mail from a domain without a DMARC policy
- 550 5.7.29 550 5.7.29: Gmail blocked a message not sent over TLS
- 550 5.2.1 550 5.2.1: the email account that you tried to reach is inactive
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