Complaint rate
Also known as: Spam complaint rate, Abuse rate
Definition
Complaint rate is the proportion of delivered messages that recipients mark as spam, and it must stay below 0.1% — Gmail's bulk-sender rules treat 0.3% as the enforcement line.
Thresholds
| Healthy | under 0.1% |
|---|---|
| Warning | 0.1–0.5% |
| Gmail enforcement | 0.3% |
| Critical | above 0.5% |
Why it matters
Complaint rate is the more dangerous deliverability metric because the tolerance is so small. At 0.5%, one complaint per two hundred delivered messages puts an account at risk.
Complaint suppressions should be immutable. Resending to a complainant is the fastest route to a blocklisted domain.