What Is Complaint Rate?
Complaint rate is the percentage of delivered emails that recipients mark as spam. It is one of the most damaging deliverability signals: mailbox providers weigh it heavily, and a rate above roughly 0.1% (one complaint per thousand emails) can quickly push a sender into the spam folder.
Every "report spam" click is a direct negative vote from a real user, so providers treat complaints as high-confidence evidence of unwanted mail. Even a small percentage can tank inbox placement.
Keep complaint rate below 0.1%; 0.3% and above is danger territory that often triggers blocks. The best defenses are relevance and consent — send to people who expect your email, make unsubscribing effortless, and stop mailing disengaged recipients.
Feedback loops (FBLs) from providers let you capture complaints and immediately suppress those addresses. Removing complainers on the first complaint is essential to protecting reputation.
MailPilot builds reputation through genuine positive engagement rather than volume, and its placement monitoring surfaces reputation dips before complaints spiral.
Protect your reputation →