Verify every sending domain in Google Postmaster Tools. Watch spam rate (keep under 0.1%), domain reputation (medium or high) and authentication rates (near 100%). Everything else is secondary.
Setup
Add each sending domain at postmaster.google.com and verify with a TXT record. Data appears only once a domain sends enough mail to Gmail, which can take a week at cold email volumes.
The three graphs
- Spam rate. Complaints divided by delivered. Under 0.1% is healthy. 0.3% is where Google starts filtering and where mitigation is refused.
- Domain reputation. High, medium, low, bad. Low means stop and warm up. Bad rarely recovers.
- Authentication. SPF, DKIM and DMARC success rates. Anything under 95% means a configuration problem; run the domain check.
Reading it honestly
Postmaster shows Gmail only, and only for days with enough volume. No data is not good news; it means too few sends to measure. For Outlook, Microsoft SNDS gives a rougher equivalent.
Live SPF, DKIM, DMARC and MX lookup with raw records and plain-English fixes.
Questions
Why does Postmaster Tools show no data for my domain?
Volume to Gmail is below the daily threshold, or the domain was verified recently. Give it a week of sending.
What spam rate should cold email aim for?
Under 0.1%. That is one complaint per thousand delivered. At 0.3% Gmail will not consider mitigation requests.