{"id":5212,"date":"2026-08-06T10:41:44","date_gmt":"2026-08-06T10:41:44","guid":{"rendered":"https:\/\/www.mailercloud.com\/blog\/?p=5212"},"modified":"2026-08-06T10:41:44","modified_gmt":"2026-08-06T10:41:44","slug":"gmail-421-4-7-0-4-7-28-deferrals","status":"publish","type":"post","link":"https:\/\/www.mailercloud.com\/blog\/gmail-421-4-7-0-4-7-28-deferrals","title":{"rendered":"Gmail 421 4.7.0 and 4.7.28 Deferrals: What They Mean and How to Fix"},"content":{"rendered":"\n

Your queue starts backing up, delivery slows to a crawl, and your logs fill with lines like this:<\/p>\n\n\n\n

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421 4.7.0 Try again later, closing connection.<\/em><\/p>\n<\/blockquote>\n\n\n\n

Or this one, which senders find more alarming:<\/p>\n\n\n\n

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421 4.7.28 Our system has detected an unusual rate of unsolicited mail originating from your IP address. To protect our users from spam, mail sent from your IP address has been temporarily rate limited.<\/em><\/p>\n<\/blockquote>\n\n\n\n

Here is the single most important thing to understand: a 4xx response from Gmail is not a block.<\/strong> It is a throttle, and it is Google telling you something is wrong before<\/em> it becomes a block. Across Gmail’s published error table<\/a> the pattern is consistent: 4.7.x strings say “has been rate limited,” 5.7.x strings say “was blocked.” Google does not state this as a categorical rule, but every documented pair follows it. You are still in the recoverable stage \u2014 but knowing when a 4.7.x becomes a 5.7.x<\/a> is what keeps you there.<\/p>\n\n\n\n

Ultimately, what determines whether you stay there is how you respond in the next few hours. Most senders respond by retrying harder, which is precisely the behavior that converts a temporary throttle into a durable reputation problem.<\/p>\n\n\n\n

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Table of Contents<\/p>\n<\/span><\/div>\n