Definition
Complaint rate: The share of delivered messages that recipients mark as spam. Gmail asks senders to keep the rate shown in Postmaster Tools below 0.1% and never reach 0.3%, and Yahoo uses the same 0.3% ceiling.
How complaint rate is calculated
Divide spam reports by messages delivered. If 20,000 messages reach recipients and 14 people click Report spam, your complaint rate is 0.07%.
Each provider calculates it on its own traffic, so your rate at Gmail and at Yahoo can differ a lot. Use each provider's own dashboard, such as Google Postmaster Tools, as the number that counts there.
How complaints reach you through feedback loops
Yahoo, Microsoft and other providers run feedback loops that send a report to the sender, usually in the ARF format, each time a recipient marks a message as spam. Your email platform uses these to unsubscribe the complainer automatically.
Gmail does not send per-message complaints. It shows aggregate spam rates in Postmaster Tools instead, so your platform's dashboard undercounts complaints from Gmail users.
How to lower your complaint rate
Most complaints come from people who do not remember signing up or no longer want the mail. Make consent clear at signup, send what you promised at the frequency you promised, and confirm signups with double opt-in.
Make leaving easier than complaining: a visible unsubscribe link and one-click unsubscribe in the headers. Retire people who have stopped engaging before they start reporting you.
How RocketVerifier handles it
Verification keeps many likely complainers out of a send. Role-based addresses come back as risky with sub_status role_based, addresses on your suppression list and known complainers as do_not_mail, and toxic addresses as toxic, so you can leave them out. Monitors recheck SPF, DKIM, DMARC and blocklist status on a schedule and alert you when something changes.