If you’re managing a high-volume email program, and Gmail makes up a large part of your audience, Google Postmaster Tools (GPT) is one of the few official windows into your email deliverability performance. Yet it’s one of the most underutilized tools by marketing teams.

Let’s break down how to set it up, what the data means, and how you can use it to improve inbox placement.

What is Google Postmaster Tools?

Google Postmaster Tools is a free tool offered by Google that gives senders visibility into how Gmail is interpreting your email program. It surfaces data like:

• Spam complaint rates

• IP and domain reputation

• Authentication (DKIM, SPF, DMARC) pass rates

• Encryption rates

• Delivery errors

This isn’t campaign-level data. It shows how Gmail is treating your domain overall. If you want to know whether your emails are likely landing in the inbox or the spam folder for Gmail users, Google Postmaster is one of the only ways to find out. It’s Gmail’s way of telling you how much it trusts your emails.

How to set it up

1. Go to postmaster.google.com

2. Log in with a Google account

3. Add and verify your sending domain(s)
   You’ll need to verify that you own the domain by adding a small piece of text (called a DNS TXT record) to your domain settings. If you’ve ever set up email authentication (like SPF or DKIM) or verified a domain for a tool like Google or Postmark, it’s a similar process. Ask a web administrator for some help here if this doesn't sound familiar to you.

⚠️ Important: Only domains that send at high enough volume to Gmail users will populate data. If you’re sending under 1,000 messages/day to Gmail, you may not see reports.

What the dashboards show, and what to do with the data

📉 Spam rate

The percentage of emails marked as spam by Gmail users.

• Healthy: Under 0.1%

• Warning zone: 0.1% – 0.3%

• Danger zone: Over 0.3%

🛠️ What to do if it’s high: Improve list hygiene. Remove disengaged users from your regular sending and audit your segmentation and cadence.

🛡️ Domain & IP reputation

Rated as: High, Medium, Low, or Bad.

• This is Gmail’s internal trust score. A High reputation means your mail is likely landing in the inbox. Low or Bad means it’s likely going to spam.

🛠️ What to do if it drops: Stop blasting unengaged users. Make sure your authentication is passing. Use ramp-up techniques for new IPs or domains.

✅ Authentication

Shows pass rates for SPF, DKIM, and DMARC.

• 100% is the goal here.

• Failing authentication is a red flag for Gmail and may result in your emails being rejected or filtered.

🛠️ What to do if failing: Work with your ESP or dev team to fix your DNS records. Prioritize DMARC alignment for best results.

🔐 Encryption

Tracks how many of your messages are encrypted in transit (via TLS).

• Should be near 100%. Most modern ESPs handle this by default.

❌ Delivery errors

Shows if Gmail is rejecting or deferring your emails.

• Spike in errors? It may mean you’re hitting rate limits or Gmail is throttling your domain due to poor reputation.

🛠️ What to do: Check your bounce logs. Slow your sending or break sends into smaller batches.

How often should you check it?

We recommend checking Google Postmaster Tools at least once a week as part of your regular deliverability routine. But during periods of change, like warming up a new IP address, switching ESPs, or seeing drops in open rates, you should be checking daily.

During an IP warmup, GPT is one of the only tools that shows how Gmail is responding to your new sending behavior. If your domain or IP reputation stays low, you’ll likely see your emails hitting spam.

It’s especially useful for troubleshooting low open rates during warmup, helping you gauge whether inboxes are starting to trust your new infrastructure or not. It won’t give you all the answers, but it will point you in the right direction.

👉 Example: We helped Havaianas warm up a new IP after a major ESP migration. Monitoring Google Postmaster daily allowed us to spot reputation issues early and course-correct before inbox placement took a hit.

Final thoughts

Most marketers only notice deliverability issues when open rates drop. Google Postmaster Tools gives you a chance to catch problems before they show up in your metrics. It's not campaign-level granularity, but it’s essential for monitoring long-term sender health.

If you're not using GPT yet, get your domain verified today. And if you're seeing dips in reputation or spam complaints, Scalero can help you troubleshoot and rebuild trust with inbox providers.