Private email infrastructure & deliverability engineering
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NorthboundMail Systems
Est. 2011 — SMTP infrastructure & deliverability
Knowledge base

Google Postmaster Guide

How to set up Postmaster Tools, what each metric means, and how to interpret the reputation graph.

Last updated March 2025 · 8 min read

Google Postmaster Tools is the authoritative window into how Gmail scores your sending. Setup is a one-time DNS verification per sending domain, after which you get daily metrics on domain reputation, IP reputation, spam rate, feedback loop rate, authentication rate, encryption rate and delivery errors.

Setup

Add each sending domain in Postmaster Tools. Verify by TXT record. Verify subdomains separately — verification does not cascade. Below a volume threshold (a few thousand messages per day per domain to Gmail), most metrics show 'no data'.

Reading the metrics

  • Domain reputation. The single most important signal. Bad or Low = expect spam-folder placement. Medium = borderline. High = inbox.
  • IP reputation. Similar scale, per IP. Diverges from domain when you rotate IPs or share domain across pools.
  • Spam rate. User marks divided by inbox-delivered volume. 0.3% is the threshold at which Gmail's stated policy is to filter aggressively.
  • Authentication rate. Should be near 100% for SPF, DKIM and DMARC. Anything else means you have configuration drift.

What to do on a reputation drop

First identify what changed. New sending source, new list segment, new content pattern, new IP allocation. Postmaster tells you what your reputation is, not why. Correlate against your send calendar to find the trigger. Suppress the offending segment or content, and reputation typically recovers over 7–14 days if the corrective action is real.

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