Complaint rate
The share of recipients who mark your mail as spam. Mailbox providers weigh this more heavily than bounces. Even a fraction of a percent is enough to land a domain in spam.
The share of recipients who mark your mail as spam. Mailbox providers weigh this more heavily than bounces. Even a fraction of a percent is enough to land a domain in spam.
What it measures
Complaint rate is the share of delivered messages that recipients report as spam. It is the signal mailbox providers weigh most, because it is a person saying I did not want this, which a bounce or a missing open never is.
The numbers that matter
Google's sender guidelines give concrete targets for the spam rate shown in Postmaster Tools: keep it below 0.10%, and never let it reach 0.30%. At one complaint per thousand messages you are already near the line. Cold email, which lands on people who did not ask for it, starts closer to that line than permission-based mail does.
Where you can and cannot see it
- Google Postmaster Tools reports spam rate for Gmail recipients, but only above a volume threshold.
- Feedback loops from some providers forward individual complaints to you, if you are registered. See feedback loop.
- Most others tell you nothing. You infer it from falling replies and rising soft bounces and throttling.
What drives it
- Poor targeting. Wrong person, wrong company, wrong problem.
- No easy way out. If unsubscribing is hard, people hit the spam button. Bulk senders to Gmail and Yahoo are required to support one-click unsubscribe via the
List-Unsubscribeheader. See unsubscribe. - Too many follow-ups to people who stayed silent.
- Role addresses, where one of many readers can complain. See role address.
Every complaint is permanent damage to sender reputation. Prevention is cheap; recovery is slow.
Ready to try it on a real list?
The share of recipients who mark your mail as spam. Mailbox providers weigh this more heavily than bounces. Even a fraction of a percent is enough to land a domain in spam.
Get startedRelated
- Cold email & deliverability glossary
Plain-language definitions for the terms that come up in cold outreach and email deliverability: bounce rate, catch-all, SPF/DKIM/DMARC, sender reputation, and more.
- Bounce rate — cold email glossary
The share of sent emails a mail server refuses to deliver. A hard bounce means the mailbox does not exist; a soft bounce means it is temporarily unreachable.
- Hard bounce — cold email glossary
A permanent delivery failure: the mailbox does not exist, the domain does not accept mail, or the server has rejected the recipient for good. Hard bounces are the ones that wreck sender reputation.
- Soft bounce — cold email glossary
A temporary delivery failure: a full mailbox, a greylisting delay, or a receiving server that is down. Retrying can succeed; treating every soft bounce as a dead address thins a list for no reason.