Deliverability is mostly inference. You send, you watch reply rates, you guess at what the filters are doing.
Google Postmaster Tools is the exception. It is Gmail telling you, directly, what it thinks of your domain, reputation, spam rate, authentication success, delivery errors. It is free, it takes ten minutes per domain, and a surprising number of teams running serious cold email have never set it up.
What it gives you
Domain reputation. Rated High, Medium, Low or Bad. The single most useful number available to a cold sender, because it is Gmail’s own assessment rather than a third party modelling it.
IP reputation. Same scale, for your sending IPs. Relevant mainly if you are on dedicated IPs; on a shared pool this reflects the pool.
Spam rate. The proportion of your Gmail recipients marking you as spam. This is the number that matters most, Gmail’s bulk sender requirements set 0.3% as the threshold you must stay under, and 0.1% is the figure to actually aim for.
Authentication results. SPF, DKIM and DMARC pass rates as percentages. Anything under 100% means something is misconfigured for part of your mail.
Encryption and delivery errors. TLS rates and the reasons Gmail rejected or deferred mail.
Feedback loop. Complaint data for senders using Gmail’s FBL identifier.
Setting it up
Per sending domain, not per mailbox.
- Go to postmaster.google.com and add your sending domain.
- Gmail gives you a TXT record. Add it to that domain’s DNS.
- Verify. Usually minutes, occasionally an hour.
- Repeat for every sending domain.
That last step is where cold senders stall. If you run 30 sending domains, this is 30 verifications, and there is no bulk method. It is tedious and it is a one-time cost.
The practical shortcut: set it up for your three or four highest-volume domains rather than all thirty. The data populates on volume anyway, and a sample of your estate tells you most of what you need. Add the rest as they grow.
The volume problem
Here is the catch that limits this tool for many cold senders.
Postmaster Tools needs roughly a few hundred messages a day to the same Gmail domain before data populates. Below that, you see empty charts.
A cold email estate running three mailboxes per domain at 40 sends a day is 120 a day per domain, and perhaps a third of those go to Gmail addresses. That is below the threshold, and the dashboard stays blank.
So the realistic picture:
| Setup | Will you see data? |
|---|---|
| High-volume domain, 500+/day | Yes, reliably |
| Moderate, 200–500/day | Partially, patchy |
| Typical cold estate, 100/day per domain | Usually not |
| Consolidated reporting across domains | Not supported |
This is a real limitation and worth stating plainly, because advice telling cold senders to “just use Postmaster Tools” frequently ignores it. The tool is built for bulk senders with concentrated volume, not for estates that deliberately spread volume thin.
What to do about it: if your domains are individually below the threshold, Postmaster Tools is not your primary instrument. Inbox placement testing is, because it works at any volume. Use Postmaster for the domains that do clear the bar and treat it as confirmation rather than your main signal.
Reading the numbers
Domain reputation: High, nothing to do.
Medium, a warning. Something is drifting. Check spam rate and recent volume changes before it becomes Low.
Low, mail is being filtered. Act now: pause the campaigns driving it, check bounce rate and list sourcing.
Bad, most mail is going to spam. Stop sending from this domain. Recovery takes weeks of reduced, well-targeted volume, and some domains do not come back.
Spam rate above 0.3%, you are over Gmail’s stated threshold. This is not a soft signal; it is the line in their published bulk sender requirements.
Spam rate 0.1%–0.3%, survivable but drifting. Targeting is the cause, not copy.
Authentication under 100%, some portion of your mail is failing SPF, DKIM or DMARC. Most commonly an SPF record over the ten-lookup limit, which fails silently. SPF, DKIM and DMARC explained covers the fix.
What it will not tell you
Worth being clear, because it gets over-relied on as much as it gets skipped.
Where your mail landed. Reputation is not placement. A domain with Medium reputation may still be reaching Primary; a High-reputation domain can land in Promotions. For folder-level answers you need an inbox placement test.
Anything about Microsoft. Outlook and Microsoft 365 are a large share of B2B recipients and Google tells you nothing about them. Microsoft SNDS covers IP-level data; there is no domain-level equivalent.
Anything about corporate gateways. Mimecast, Proofpoint and similar filter a meaningful share of enterprise mail and report nothing.
Why. It tells you reputation is Low. It does not say which campaign, segment or list caused it. You correlate that yourself against your own sending history.
A sensible routine
At setup: add your main sending domains, confirm authentication shows 100%.
Weekly: check spam rate and reputation on the domains that have data. Five minutes.
On any change: after adding domains, changing infrastructure or increasing volume, watch for a fortnight.
When reputation drops: correlate against your sending log. What changed two weeks before the drop? New list source, volume increase, new campaign? Reputation lags behaviour, so look back rather than at today.
That lag is the most useful thing to internalise. By the time the dashboard turns Medium, the cause is roughly a fortnight old.
Where it sits in the stack
Postmaster Tools is one of four instruments, and it is the cheapest:
| Tool | Cost | Tells you |
|---|---|---|
| Authentication checker | Free | Whether records are valid |
| Postmaster Tools | Free | What Gmail thinks of your domain |
| Inbox placement test | Paid or included | Which folder, per provider |
| Blocklist monitor | Free to cheap | Whether you are listed |
Two of the four are free and most teams run neither. Which deliverability tools do what covers the full map and the order to buy in.
The short version
Google Postmaster Tools is the only direct feedback Gmail gives senders, it is free, and setup is ten minutes per domain.
The limitation that matters for cold senders: it needs a few hundred messages a day per domain before data appears, and a typical estate spreading volume across many domains sits below that. Set it up for your highest-volume domains and treat placement testing as your primary instrument.
Watch spam rate above everything, 0.3% is Gmail’s published line, 0.1% is the target. Authentication under 100% means something is silently broken.
And remember reputation lags behaviour by roughly a fortnight. When it drops, look at what changed two weeks ago, not today.
Next: what sender reputation actually is, or how to run an inbox placement test.
Frequently asked questions
What is Google Postmaster Tools?
A free Google service reporting domain reputation, IP reputation, spam rate, authentication pass rates and delivery errors for mail sent to Gmail. It is the only direct feedback Gmail provides to senders.
Why is my Postmaster Tools dashboard empty?
Volume. Data needs roughly a few hundred messages a day to Gmail from the same domain before it populates. Cold email estates that spread volume across many domains frequently sit below that threshold.
What spam rate is acceptable in Postmaster Tools?
Gmail’s bulk sender requirements set 0.3% as the threshold. Aim for under 0.1%. Between those two figures you are survivable but drifting, and targeting rather than copy is usually the cause.
Does Postmaster Tools show whether emails land in spam?
No. It reports reputation, not placement. A domain can have High reputation and still land in Promotions. For folder-level results per provider you need an inbox placement test.