The free window into Gmail's file on you. Postmaster Tools shows the data Gmail actually uses to route your mail — domain reputation, spam rate, authentication pass rate, and more. If you send to any Gmail addresses, this is the first place to look.
Google Postmaster Tools is a free dashboard that shows how Gmail sees your sending domain. It is not a general email analytics tool — it only shows Gmail-specific data, and only for domains sending significant volume to Gmail accounts. If you send fewer than a few hundred emails per day to Gmail, some graphs may be blank.
You set it up by verifying ownership of your domain in the Postmaster Tools console at postmaster.google.com. Verification requires adding a TXT record to your DNS.
This is the single most important graph. Gmail rates your domain on a four-point scale: High, Medium, Low, and Bad.
Domain reputation recovers slowly. Moving from Bad to Medium can take weeks of clean sending. There is no shortcut.
This shows the percentage of your mail that Gmail users are marking as spam. The threshold you need to stay below is 0.10% — above that you are in a warning zone. Above 0.30% consistently and Gmail will route most of your mail to spam.
Similar to domain reputation but tracked at the sending IP level. If you are on a shared IP (common with many ESPs), your IP reputation is partly influenced by other senders on the same pool. If you have dedicated IPs, this is entirely in your control.
Shows the percentage of your mail passing SPF, DKIM, and DMARC checks. If this number is below 100%, you have unauthorised sending sources — systems sending as your domain that you haven't explicitly authorised.
Target: 100% SPF, 100% DKIM, 100% DMARC. Anything less means mail that could be failing authentication and contributing to reputation damage.
Shows rejected or deferred messages. Spikes here indicate temporary or permanent blocks from Gmail — often caused by a sudden increase in sending volume, a large batch to a low-engagement list, or a technical problem with your sending infrastructure.
The most useful thing about Postmaster Tools is the trend, not the snapshot. A domain reputation that is High today but was Low a month ago tells you something different from one that has been High for two years. Look at 30-90 day windows to understand the trajectory.
Spikes in spam rate that correlate with specific campaigns are the most actionable signal — they tell you exactly which list segment or content triggered complaints.
Postmaster Tools only shows Gmail data. It tells you nothing about Outlook, Yahoo, or any other provider. For a complete picture you need Microsoft SNDS for Outlook data, and seed testing tools for other providers.
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