The sender used a new shared IP that previously sent crypto spam. Google’s IP reputation cache carried over.

This report is structured for IT administrators, email marketers, and developers who need to understand why emails are blocked, how to diagnose the issue, and how to prevent it. 1. Executive Summary Gmail (Google Workspace & personal @gmail.com) blocks or filters over 10 billion emails per day —roughly 85% of all inbound traffic. “Blocked” does not always mean a hard rejection (bounce). It encompasses three distinct states: Hard Bounce (explicit block), Soft Bounce (temporary deferral), and Silent Drop (spam folder).

increase(smtp_550_5_7_1_total[5m]) > 10 Scenario: A tech newsletter with 95% open rate suddenly gets blocked by Gmail.

status=bounced (host gmail-smtp-in.l.google.com[142.250.125.27] said: 550-5.7.1 Our system has detected an unusual rate of unsolicited mail) Or in the header of a delivered email:

Blocked Emails Gmail Page

The sender used a new shared IP that previously sent crypto spam. Google’s IP reputation cache carried over.

increase(smtp_550_5_7_1_total[5m]) > 10 Scenario: A tech newsletter with 95% open rate suddenly gets blocked by Gmail. The sender used a new shared IP that

status=bounced (host gmail-smtp-in.l.google.com[142.250.125.27] said: 550-5.7.1 Our system has detected an unusual rate of unsolicited mail) Or in the header of a delivered email: It encompasses three distinct states: Hard Bounce (explicit

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