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Glossary
Complaint rate (spam rate)
The percentage of recipients who hit the "report spam" button. Even tiny rates matter — under 0.1%.
When a recipient marks your email as spam, the mailbox provider records a feedback-loop event. Aggregate this across many sends and you get the complaint rate (or "spam rate" in Postmaster terminology).
Gmail and Outlook tolerate roughly 0.1% before they start downgrading your inbox placement. Above 0.3% you'll start seeing bulk spam-folder placement; above 0.5% and you risk domain-wide blocks.
BoomSauce treats complaint rate as a leading indicator — auto-pausing at 0.1% gives you headroom to fix before the damage compounds.
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