The Deliverability Ledger · Google · 6 posts
Gmail bounces and the sender rules
The Gmail bounces senders hit most (421 4.7.0, 421 4.7.28, 550 5.7.26), the bulk sender requirements, Postmaster Tools, and the way back out of the spam folder.
All 6, newest first
- 421 4.7.28 “Our system has detected an unusual rate of unsolicited mail originating from your IP address” — Gmail Fix GuideGmail's 421 4.7.28 is a temporary IP-reputation throttle, separate from blocklists and authentication failures. Here's exactly what each piece of the bounce means and the step-by-step fix.
- 421 4.7.0 “Try again later, closing connection” — Gmail Rate Limit DecodedGmail's 421 4.7.0 is a temporary deferral, but the trigger varies. Here's how to tell whether it's volume, reputation, or per-connection limits, and how to fix each.
- 550 5.7.26 “This message does not have authentication information” — Gmail Fix GuideGmail's 550 5.7.26 bounce means your mail failed Gmail's bulk-sender authentication checks. Here's exactly which check is failing and the precise fix for each one.
- Emails Going to Spam in Gmail? The 2026 Recovery PlaybookIf Gmail is filing your emails into spam, the cause is one of seven specific things. Here's the diagnostic sequence and the 30-day recovery playbook.
- Gmail & Yahoo Bulk Sender Requirements: Complete 2026 Compliance GuideSince February 2024, Gmail and Yahoo enforce strict requirements on bulk senders. Here's the complete 2026 compliance checklist: authentication, unsubscribe, and the 0.3% spam ceiling.
- Google Postmaster Tools: The Complete Guide for Senders in 2026Google Postmaster Tools is the only place Gmail tells you what it actually thinks of your sending. Here's how to set it up, verify, and read every dashboard like a deliverability pro.
Other topics
- DeliverabilityThe signals inbox providers weigh, what each SMTP code and bounce type means, list hygiene, warm-up, and the numbers to measure yourself against.
- MicrosoftThe 550 and 421 errors Microsoft returns, how Exchange Online Protection scores a message, SNDS and JMRP, and how to get off the Outlook blocklist.
- BlacklistsHow to tell if you are listed, why IP and domain blacklists catch different things, and what SURBL listings mean for cold email.
- AuthenticationSetting up SPF, DKIM and DMARC step by step, and choosing between a quarantine and a reject policy.
- YahooThe two refusals Yahoo and AOL send most, 421 [TSS04] for complaints and 554 5.7.9 for policy, and how to clear each.
- Cold EmailGetting cold outreach into the inbox without burning the domain it is sent from.
- ReputationThe usual reasons a sender reputation drops, and how to rebuild it.
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