sender reputation
How sender-reputation scoring actually works
Reputation is not a single number. It is a bundle of signals a mailbox provider watches per domain and per IP — and crossing one threshold can silently move you to spam.
2026-06-08 · 7 min read
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Ask five people what "sender reputation" means and you get five different answers. Underneath, mailbox providers like Gmail expose (via Postmaster Tools) a specific set of signals, and it is worth knowing what each one actually measures.
The signals that matter
- Spam rate — the share of your delivered mail users mark as spam. Gmail treats anything sustained above roughly 0.3% as a warning sign and 0.1% as the safe ceiling to stay under.
- IP reputation and domain reputation — tracked separately; a good domain on a bad shared IP (or vice versa) still gets flagged.
- Authentication rate — the share of your mail that passes SPF/DKIM/DMARC alignment cleanly. See SPF, DKIM & DMARC explained if any of that is unfamiliar.
- Delivery errors — the rate of temporary and permanent failures, which spikes when you keep mailing bounced or invalid addresses.
- Feedback loop / user-reported spam — direct complaint signals from mailbox providers that supply them.
Why one bad batch can sink a whole domain
These signals are aggregated per sending domain (and per IP) over a rolling window, not per campaign. Send one poorly targeted batch that spikes complaints, and the resulting reputation dip applies to every message that domain sends afterward — including the good ones. That is why "just send more carefully next time" does not undo the damage; the domain needs time, or a fresh one, to recover.
Why a circuit-breaker beats a dashboard
Postmaster Tools shows you the damage after receivers have already reacted — usually with a day or more of lag. By the time a human notices the spam-rate graph ticking up, the domain has often already been sending degraded mail for hours. A reputation circuit-breaker watches the same signals continuously and pauses the domain automatically the moment it drifts past a safe threshold, instead of waiting for someone to check a dashboard.
For the full authentication and warmup picture, see the deliverability checklist and what a warmed sender pool is. Or check your own domain right now with the free SPF checker and blacklist checker.
Want CogniLead running deliverability on every send? Try it free or read the docs.