What are some known specific bounce messages from Gmail?
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You send a batch of emails, a chunk bounces back from Gmail, and your ESP log shows a wall of codes like 550-5.7.26 or 421-4.7.0. Good news: Gmail is one of the most talkative providers out there. Its bounce messages are specific enough that you can usually tell exactly what went wrong without any guesswork.
Here are the most common Gmail bounce codes and what they actually mean for you.
Authentication failures
550-5.7.26. "This message does not have authentication information or fails to pass authentication checks." This one almost always points to a missing or broken DKIM signature, a DMARC policy blocking unauthenticated mail, or a misaligned SPF record. If you're seeing this, DKIM and DMARC are the first things to check.
550-5.7.1 (auth variant). "Messages missing a valid DKIM signature." Narrower than the one above. Your domain is sending without a DKIM signature that Gmail can verify. Check your signing domain and selector.
Spam and policy rejections
550-5.7.1 (spam variant). "Our system has detected that this message is likely spam." This is Gmail's content or reputation filter firing. It can mean your sending IP has a poor history, your content triggered a filter, or your engagement rates are low enough that Gmail has lost trust in your mail.
421-4.7.0. "Our system has detected an unusual rate of unsolicited mail originating from your IP address." This is a soft bounce. Gmail isn't rejecting you permanently yet, but it's throttling you hard and asking you to slow down. Continuing to hammer sends while seeing this code will make things worse.
Rate limiting
421-4.7.0 (rate variant). "Try again later." A temporary deferral. Your sending volume or frequency crossed a threshold Gmail set for your IP or domain. Most ESPs will retry automatically, but if it keeps recurring, you need to warm your sending infrastructure more carefully or reduce your send cadence.
452-4.5.3. "Domain policy size per transaction exceeded." You're hitting too many recipients per connection. Split your batches into smaller transactions.
User and mailbox issues
550-5.1.1. "The email account that you tried to reach does not exist." A hard bounce. That address is gone. Remove it from your list immediately. Continuing to send to it damages your sender reputation.
552-5.2.2. "The recipient's inbox is full." A temporary failure, not a fatal one. Gmail will usually retry delivery for a few days. That said, a full inbox often means the account is abandoned, so watch whether this converts to a 5.1.1 over time.
One thing that makes Gmail's bounce messages particularly useful: they often include a link to support.google.com/mail/answer/... with the specific policy or guideline that triggered the rejection. Don't skip that link. It usually tells you exactly what Gmail wants you to fix.
And if you're seeing a Gmail bounce code that isn't here or the fix isn't obvious, our SOS hotline is free. We can read the full message with you and figure out the right next step.
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