Postmaster Tools — the lagged truth
Free dashboards from Google, Microsoft, and others that show your sending health from the receiver's side. 24-72h lagged but invaluable.
Postmaster Tools (Google), SNDS (Microsoft), and similar dashboards from Yahoo and Apple expose your sending reputation as the receivers see it. They are 24-72 hours lagged, but they are the closest thing to ground truth available outside running your own measurement.
Setting it up — Google
Visit postmaster.google.com. Add your sending domain. Verify ownership via TXT record (separate from your DKIM and DMARC records). Wait 24-48 hours for data to populate.
Reading the data
- Spam-rate — the bucket your domain falls into. Aim for "Low".
- IP reputation — five buckets per sending IP. Watch for drops.
- Domain reputation — same five buckets, but for your sending domain.
- Authentication — SPF / DKIM / DMARC pass rates by day.
- Encryption — % of mail delivered over TLS.
- Delivery errors — top reasons mail bounced.
- Feedback loop — Gmail does not have a real FBL but exposes a "Daily volume of marked-as-spam" signal here.
Microsoft SNDS
Microsoft's Smart Network Data Services. IP-level only (no domain dashboard). Shows complaint rates, trap hits, and a daily traffic count per /24. Older UI but the data is reliable.
What to do with the data
Plot it daily. Set a threshold alert. When a metric drops, work backward: was it a specific campaign, a specific cohort, a specific IP? The Postmaster data does not tell you the cause; it confirms the symptom. The cause lives in your own send logs.