Gmail Postmaster Tools is the closest thing cold email senders get to a direct line into how Google actually sees their sending domain — and most senders who set it up never come back to read it after the initial setup.
It's a free tool from Google that reports domain reputation, spam rate, authentication pass rates, and delivery errors for any domain you verify ownership of. This is direct signal from Gmail's own systems, not a third-party estimate — when Postmaster Tools shows a problem, that's the actual data Gmail's spam filtering is using against your domain.
Go to postmaster.google.com and verify ownership via a DNS TXT record — the same verification pattern used for most Google services. Set this up for every domain you send from, not just your primary one; each domain's reputation is tracked entirely separately, so a Postmaster Tools account for only one domain leaves the rest of your infrastructure unmonitored.
| Reputation level | What it means |
|---|---|
| High | Strong sending history, minimal spam signals |
| Medium | Acceptable but not exemplary — worth investigating what's holding it back |
| Low | Real deliverability risk — expect spam-folder placement to increase |
| Bad | Active deliverability failure — treat as urgent |
A new domain typically shows no data at all until it has enough send volume for Google to form a reputation assessment — absence of data isn't the same as a bad reputation, it just means the domain hasn't sent enough yet to be scored.
This shows the percentage of your sent mail marked as spam by recipients, tracked daily. Per our Google bulk sender requirements guide, the target is below 0.10%, with 0.30% as a hard enforcement threshold. Watch the trend line, not only the current number. A spam rate climbing steadily toward 0.30% over several days is worth acting on before it crosses the line, not after.
These show the percentage of your mail passing SPF, DKIM, and DMARC checks, plus what fraction is delivered over encrypted (TLS) connections. Any of these sitting meaningfully below 100% indicates a real configuration problem worth fixing immediately — authentication failures are entirely within your control to fix, unlike some reputation factors that take time to recover.
Check Postmaster Tools weekly at minimum, and immediately after any campaign that felt different — a new list source, a higher-than-usual send volume, a new sequence template. Catching a reputation dip early, while it's still in "medium" rather than "low" or "bad," is meaningfully easier to recover from than waiting until deliverability problems are already visible in reply rates.
Domain reputation (high/medium/low/bad), spam rate, SPF/DKIM/DMARC authentication pass rates, TLS encryption rate, and delivery errors — all reported directly from Google's own systems for any domain you've verified ownership of.
Verify domain ownership at postmaster.google.com via a DNS TXT record, the same pattern used for other Google service verifications. It should be set up separately for every sending domain, since reputation is tracked per domain.
Below 0.10% is the target. Above 0.30% is Google's hard enforcement threshold, at which point a domain becomes ineligible for mitigation support until spam rate stays under 0.30% for 7 consecutive days.
A domain needs enough send volume before Google can form a reputation assessment — no data isn't the same as a bad reputation, it just means the domain hasn't sent enough yet to be scored.
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Written by
Scott Holmes
AI systems consultant based in Barrie, Ontario. Founder of Pinnacle Tech Projects. Has monitored domain reputation through Google Postmaster Tools across dozens of sending domains.
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