Google Postmaster Tools is a free service that reports how Gmail treats mail from a domain you own. You verify the domain, and Google shows you dashboards built from the mail it received. It is the closest thing to a direct channel to one mailbox provider, and it is worth being precise about what it does and does not cover.
What is actually being measured?
Mail to personal Gmail accounts, mostly authenticated with DKIM, aggregated per domain.
Google states the scope in its own description of the dashboards, and each qualifier matters:
Postmaster Tools dashboards let you view various data about outgoing email you send to personal Gmail accounts, including data about spam rate, reputation, message authentication, and delivery errors.
Several caveats come with the data, and they explain most of the confusing readings people report:
- Postmaster Tools attempts to exclude all forwarded messages from dashboard data, however it’s possible that some dashboards include data from forwarded messages.
- Dashboard data isn’t real-time data. When you make changes to your outgoing email, the changes aren’t immediately reflected in dashboard data. Typically, the data is updated within 24 hours but can take longer.
- Some dashboards show data only for messages authenticated with DKIM.
- To protect the privacy of Gmail users, dashboards might not include all data on days when your outgoing email volume is low. This can impact what you see in the dashboards.
The volume caveat is the one that frustrates smaller senders: below a certain daily volume the dashboards stay empty, and there is no threshold published. Google's own troubleshooting advice is simply to "Check the dashboards again when your email sending volume increases enough to populate the dashboards."
What do the dashboards show?
Eight of them, each answering something different.
| Dashboard | What it reports |
|---|---|
| Compliance status | Whether you meet each sender requirement, graded individually |
| Spam rate | The percent of your messages recipients marked as spam by hand |
| IP reputation | A quality rating for the IP addresses you send from |
| Domain reputation | A quality rating for the domains you send from |
| Feedback loop | Campaign messages recipients marked as spam, grouped by an identifier you set |
| Authentication | The percent of your mail passing SPF, DKIM and DMARC |
| Encryption | The percent of your mail sent over an encrypted connection |
| Delivery errors | The percent of authenticated messages rejected or temporarily failed |
Compliance status is the one to open first. It grades each requirement as Compliant, Needs work, or No data found, which turns "our mail is going to spam" into a specific failing item. The Gmail and Yahoo requirements covers what each requirement is.
Spam rate is narrower than its name. It counts only manual reports on mail that reached an inbox, which is why it can read low precisely when things are worst. What is a spam complaint rate has the mechanics.
How do I read the reputation ratings?
As four named bands, with definitions Google publishes verbatim:
Bad: History of sending a high volume of spam regularly. Email from this domain or address is almost always marked as spam or rejected by the receiving server.
Low: History of sending a significant volume of spam regularly. Email from this domain or address is likely to be marked as spam.
Medium: History of sending legitimate email, but occasionally sends spam. Most email from this domain or address has a fair deliverability rate, except when there's a notable increase in spam.
High: History of very low spam rates, and complies with Gmail's sender guidelines. Email from this domain or address is rarely marked as spam by Gmail.
Two structural points. The rating is computed from DKIM-authenticated mail, falling back to SPF-authenticated mail if you do not sign, so unauthenticated mail is invisible to it. And the domain reputation dashboard "only displays messages sent from the exact domain used for DKIM and SPF authentication", which means a subdomain's reputation is its own and not the apex's.
There is a bigger caveat, and it is Google's own. These two dashboards are on their way out. In its notice about the interface change, Google says that in the new version "All the dashboards in old Postmaster Tools are available in v2, with the exception of the Domain and IP Reputation dashboards, which will be retired", and gives its reasoning:
- Reputation data is not easily actionable for most senders.
- Changes in sender behavior are slow to reflect in the existing dashboard.
- The current dashboard can be misleading as reputation is only one of many factors affecting deliverability.
The same notice says the v1 API is being retired now that v2 has launched, and that v2 covers everything except domain and IP reputation. So if you have built alerting on a reputation figure, it is worth knowing that the provider who publishes it considers it the least actionable thing they show you.
Why does the dashboard disagree with itself?
Because the dashboards are computed from slightly different data, and Google says so.
Compliance status in particular is not derived the same way as the others:
- The Compliance status dashboard uses a rolling data average that’s gathered over multiple days, and so your domain status might not update immediately.
- The Compliance status dashboard uses slightly different datasets than other dashboards to calculate compliance. So, data can vary slightly across dashboards.
- The Compliance status dashboard shows compliance for primary domains only. However, data from both primary and subdomains are used to determine compliance for the primary domain.
The recommended response to almost every disagreement is the same: wait seven days and look again. That is a genuinely long feedback loop, and it is the reason to fix causes deliberately rather than to change three things at once and watch.
Is it enough on its own?
No, for one structural reason: it only sees Gmail.
If half your list is at a corporate domain running its own filtering, or at Outlook, Postmaster Tools has nothing to say about them. It is the best free signal available for a large share of most consumer lists, and it is still one provider's view.
Pair it with a measurement that covers the others. Placement testing through seed accounts reports per-provider inbox and spam rates rather than one provider's opinion, which is what Bird's Inbox Insights does, and sender reputation monitoring covers what to watch between the two.