Rate the last period
How it works
Rates
Complaints and unsubscribes are divided by delivered mail; bounces by sent. Delivered defaults to sent minus bounces.
Lines
Google's published thresholds: keep spam rate under 0.1%, never above 0.3%; hard bounces under 2%. Yahoo and Microsoft apply similar bands.
Headroom
How many more complaints or bounces fit under each line this period and on the next campaign at the same rates.
What-if
The same numbers with a verified, pruned list — the change that moves the rates most.
The two numbers Google publishes
Gmail's sender guidelines are unusually specific: keep your spam rate under 0.1%, and never let it reach 0.3%. Above 0.3% Gmail starts rejecting mail from the domain, and the block persists until the rate has been under 0.1% for a period. Hard bounces are the other line — around 2% is where receivers decide the sender does not know who they are mailing. Yahoo published the same complaint thresholds; Microsoft does not publish numbers but behaves similarly. These are not soft signals; they are the levels at which the switches flip.
Why the headroom number matters
Percentages hide how few people are involved. On ten thousand delivered messages, 0.3% is thirty complaints. Thirty people clicking "report spam" — out of ten thousand who received a cold email — is not a hostile audience, it is a Tuesday. The headroom table turns the percentage into a count so the next campaign is sized against it: if you have eleven complaints of room and the last campaign produced fourteen, the next one at the same size will cross the line.
Gmail measures Gmail
Postmaster Tools reports the spam rate on mail to Gmail users only, and that is the rate the threshold applies to. If 45% of the list is on Gmail and complaints spread evenly, the Gmail-only rate is what the tool estimates; in practice Gmail users complain more readily than corporate users behind a gateway, so the real figure is higher. Treat the estimate as a floor and read Postmaster Tools for the number that counts.
What moves the numbers
List quality, before anything else. Verifying the list before sending removes most hard bounces, and hard bounces correlate with complaints because the same careless sourcing produces both. Removing unengaged contacts — no reply, no open across two campaigns — cuts complaints disproportionately, because complaints come from people who did not want the first message either. Volume per inbox is the third lever: the same list at half the daily rate produces fewer complaints per day, which is what the rolling measurement sees. Copy is fourth. It is the one everyone changes first.
Frequently asked questions
What spam complaint rate is acceptable?
Under 0.1% is Google's target; 0.3% is the line above which Gmail blocks. On ten thousand delivered messages that is ten and thirty complaints respectively.
What bounce rate is too high?
Hard bounces over 2% of sends. Above that, receivers score the sender as careless. A verified list runs well under 1%.
Where do I see my real spam rate?
Google Postmaster Tools, for the domain, on mail to Gmail. Sending tools show complaints they receive through feedback loops, which is a subset.
Do unsubscribes count against me?
Not directly — an unsubscribe is the safe exit and bulk-sender rules require offering it. But a high unsubscribe rate predicts complaints, because both come from a list that did not want the mail.
Does this apply to cold email or only marketing?
The thresholds apply to every sender. Cold email is measured the same way, and a cold list produces more complaints per thousand than an opted-in one, which is why volume and list quality matter more.
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