What Is a Complaint Rate?
TL;DR
Complaint rate is the share of delivered messages that recipients mark as spam. Google publishes the thresholds most senders work to: keep the spam rate reported in Postmaster Tools below 0.10% and avoid ever reaching 0.30%, with 0.30% also stated as the ceiling in the Gmail bulk sender requirements.
What complaint rate is too high?
Google is the only major provider publishing a number, and it publishes two. The guidance for monitoring is to stay below 0.10% and never reach 0.30% or higher; the sender requirements state the same 0.30% as a requirement. Both are measured against Gmail traffic only, in Postmaster Tools, and neither is a figure other providers commit to.
The gap between the two numbers is the useful part. 0.10% is the level Google tells senders to stay under, and 0.30% is the level it tells them never to reach, so a rate drifting past the first is the warning that exists precisely so you never test the second.
Why is a complaint worse than a bounce?
A bounce says the address was wrong. A complaint says a real person read the sender and the subject and decided the message should not have been sent, which is the exact judgment the filter is trying to predict, delivered by the one witness it trusts most.
It also compounds. Complaints train the filter on the domain, so a campaign that draws them makes the next campaign harder for every mailbox on the same sending domain, including the replies your account managers depend on.
Where do you see your complaint rate?
Per provider, from the provider. Google Postmaster Tools reports a spam rate for Gmail traffic, Yahoo reports through its Complaint Feedback Loop and postmaster tooling, and Microsoft reports complaint volume through the Junk Mail Reporting Program with IP-level data in Smart Network Data Services.
There is no combined figure, and nothing on the sending side can produce one. A sending tool can only count the complaints that were reported back to it, which means the true rate is always at least what you can see.
Frequently asked questions
It raises them. A recipient who wants out and cannot find a way out uses the spam button, which reports to the provider instead of to you. A visible opt-out is the cheapest way to convert a complaint into a suppression.