Google Postmaster Tools: What It Shows and What to Do About It

Google Postmaster Tools is a free service from Gmail that shows senders how their mail performs with Gmail users: spam complaint rates, authentication results, delivery errors and compliance with Google’s sender requirements. You add and verify a sending domain through DNS, and Gmail reports data for it once the domain sends enough mail to produce meaningful figures.

It is designed for higher-volume senders. A business sending a handful of messages a day may verify the domain and see no data, which does not mean anything is wrong.

Sign in with a Google account, add the domain you send from — the one in the From address or the DKIM signing domain — and add the verification TXT record Google provides to DNS. Verify each domain and subdomain you send from separately if you want separate reporting.

Give access to the people who manage email operations, and note the setup in your sender inventory so it is not lost when someone leaves.

The spam rate report shows the share of delivered mail that Gmail users marked as spam. Google’s email sender guidelines ask bulk senders to keep spam rates low and warn of consequences above set thresholds, so this is the number to monitor weekly. Authentication and compliance views show whether SPF, DKIM and DMARC are passing and aligned.

Delivery error data shows rejected or temporarily failed mail and the reason, which helps separate authentication problems from reputation or rate-limiting issues.

Start with what changed on your side: a new list source, a re-engagement campaign to old contacts, a higher sending frequency, a new platform or a DNS edit. Spam rate spikes usually follow a specific send; find it and stop repeating it.

Separate streams. If marketing and transactional mail share a domain, a marketing spike can hurt password resets and invoices. Using distinct subdomains for different purposes makes both diagnosis and protection easier.