Updated · 9 min read
Google Postmaster Tools: a walkthrough for people who actually send email
Picture the Monday morning where a chunk of your audience didn't get the email — not the unsubscribed chunk, not the bounced chunk, the silently-routed-to-spam chunk that your ESP dashboard happily reports as "delivered." That happens at Gmail more than anywhere else, because Gmail handles roughly 40% of global inbox share. Postmaster Tools is the only public window Google gives you into how it sees your sending domain. Free. Ten minutes to set up. Ignored by most programs. This is the walkthrough of every tab worth watching, what to do with the data when it shows up, and which charts to stop staring at.
By Justin Williames
Founder, Orbit · 10+ years in lifecycle marketing
Getting Postmaster pointed at your domain
Head to postmaster.google.com and sign in with a Google account tied to the domain you send from. Add your sending domain — marketing.brand.com, say. Gmail asks you to publish a TXT record (a small piece of verification text in your domain's DNS — the lookup table that tells the internet what belongs to you), the same pattern as Search Console. Drop it in, wait a few minutes, you're verified.
Add each subdomain separately. Reputation — Gmail's running judgement of whether your mail is wanted — is scored per subdomain, which means marketing.brand.com and accounts.brand.com need their own Postmaster entries. Two people minimum on the access list: the CRM lead and someone on the engineering side who owns DNS. Access runs through individual Google Workspace accounts, not shared logins, so document the handoff. A Postmaster lapse — forgotten login, nobody monitoring — is exactly how reputation drifts six weeks without anyone noticing.
Data starts flowing 24 to 48 hours after verification, but the charts need minimum volume — a few hundred Gmail recipients per day — before they populate meaningfully. Below that, everything is blank or sparse. Which is information too: you don't have a Gmail deliverability problem yet because you don't have meaningful Gmail volume yet.
The one chart that decides whether your mail lands
Open Postmaster and your eye should go to one place: Domain Reputation. It rates your sending domain on a four-tier scale — Bad, Low, Medium, High — and it's the single chart that decides whether Gmail trusts your mail enough to drop it in the inbox or send it sideways into spam. Every other tab in Postmaster is secondary to this one.
High means inbox placement on Gmail is effectively solved. Medium means it's fine most of the time. Low or Bad means 40% of your audience has a problem you can't see from the ESP dashboard.
What to act on, in order of severity:
High, holding steady: nothing to do. Keep doing what you're doing.
Medium climbing to High: you're improving. Don't change anything.
High drifting to Medium: investigate the last two weeks. Frequency bump, new segment, a subject line that spiked unsubscribes. Catch it now before it drops further — reputation moves quickly down and slowly up.
Medium drifting to Low: urgent. Cut to users who opened or clicked in the last 30 days. Audit the list for dormants.
Low or Bad: stop broad sending entirely. Engaged-only until it recovers.
Medium by itself isn't bad, by the way. Gmail delivers most of your mail to the inbox on Medium and applies more scrutiny to borderline cases. High is better but not essential. The thing to panic about is direction, not absolute level — a Medium that's held for months without moving is fine; a High that just dropped to Medium last week is the signal. The rating runs on rolling 7-day windows, so a spike in spam complaints can drop you a full tier inside a week.
IP Reputation — interesting, mostly not actionable
Same Bad/Low/Medium/High scale, but for the sending IPs (the numerical addresses of the servers that physically push your mail out) associated with your domain. On a dedicated IP — one your program owns alone — this tracks closely with your domain reputation. On a shared IP — most smaller programs, where your ESP pools you in with other senders — it reflects the pool, which means your neighbours' behaviour as much as yours.
In 2026, Gmail weighs domain reputation more heavily than IP reputation. Worth monitoring. Secondary to everything in the previous section.
Spam Rate — the number Gmail is actually scoring you on
Spam Rate is the percentage of your Gmail-delivered mail that recipients flagged by hitting "Report spam." It's the most direct signal Gmail uses to set your reputation, which means it's the number to watch weekly even when everything else looks fine.
Below 0.1%: healthy. No concern.
0.1–0.3%: warning zone. Gmail is starting to treat you as spam-adjacent. Investigate frequency, unsubscribe flow, dormant audience.
Above 0.3%:emergency. Gmail will route your mail to the spam folder or reject it at the door. Cut immediately to the top 20% engaged slice and go find the root cause — new segment, frequency change, a campaign that over-indexed on complaints. Recovery is 6 to 12 weeks once the rate comes back down. That's not a typo.
Gmail, uniquely among major mailbox providers, doesn't give you a feedback loop — the per-recipient list of who hit "Report spam" that other providers (Yahoo, Microsoft, AOL, Comcast) hand back through your ESP. With Gmail you see the aggregate rate and that's it. No names. Annoying but fixed policy. The spam complaints playbook covers the four levers that actually reduce the rate; Postmaster's Spam Rate is the canonical measurement.
Authentication — should be boring, panic if it isn't
The Authentication tab shows pass rates for the three protocols that prove your mail is really from you: SPF, DKIM, and DMARC — the cryptographic and DNS-based checks Gmail runs on every inbound message to confirm the sender isn't a forger. All three should sit at or near 100% on Gmail-delivered mail. If they don't, something in your setup is broken.
If SPF drops, check that your ESP's sending servers are listed in your SPF record. If DKIM drops, check DKIM signing is on in the ESP and the selector — the lookup name your ESP gave you to publish — is published in your DNS. If DMARC drops, check your policy and alignment. Rates below 95% mean authenticated mail is failing a check somewhere — almost always a config issue, almost always easy to fix once you can see which of the three has slipped. The SPF/DKIM/DMARC explainer covers each protocol in detail.
Delivery Errors — where Gmail slammed the door
Delivery Errors shows the percentage of your mail Gmail refused at the SMTP level (the conversation between your ESP's servers and Gmail's — refusal here means Gmail wouldn't even accept the message), broken down by reason. The big categories: "sender IP reputation", "policy-related", "content-related", "too-many-recipients".
In a healthy program this chart is near-empty. Gmail accepts most mail and filters at the inbox or spam-folder level rather than rejecting at the door. A spike in "sender IP reputation" rejections means your IP reputation has dropped below Gmail's acceptance floor. A spike in "policy-related" means your content is hitting specific filter rules — usually an image-to-text ratio problem or a URL shortener Gmail has flagged. Chase the spike to the category, then the category to the campaign.
How often to actually look at this
Screenshot the Domain Reputation chart weekly and keep the images in a shared drive. You want the trend, not the current state. A High that just dropped from 60 days of steady High is a very different signal from a High that just climbed from Medium, and the dashboard alone doesn't show you which one you're looking at.
The Deliverability Management skillbuilds the Postmaster check into a weekly cadence automatically. If you're running manually, put it on the calendar. Every Monday. Ten minutes. The single deliverability habit with the highest return on the time spent.
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