How to test reputation independently by domain?

Say you run marketing emails from news.harborpost.net and transactional emails from receipts.harborpost.net. Your campaign stats look fine, but password resets are landing in spam. How do you figure out which domain is the problem? You test them separately.

Here's why that matters. Domain reputation is tracked per domain by mailbox providers. If your marketing domain picks up spam complaints, that reputation doesn't automatically spread to your transactional domain. But it can, if you're not careful about mixing your sending streams. Testing them independently tells you exactly where the problem lives.

Start with Google Postmaster Tools. Add each domain separately as its own property. Once you're sending enough volume (roughly 200+ emails per day to Gmail addresses per domain), you'll get individual reputation graphs for each one. This is free, and it's the most direct signal you can get from Gmail's perspective. If one domain shows "Low" reputation and another shows "High", you've already found your answer.

Layer in a blocklist check for each domain. A domain can have good Gmail reputation and still be on a blocklist that affects delivery at other providers. Check each domain and its associated sending IPs separately. You can run a quick check with our free blocklist checker to see where things stand.

Verify authentication per domain independently. Each domain needs its own passing SPF, DKIM, and DMARC records, with no shared dependencies that could blur the signal. If domain A borrows domain B's DKIM selector, your test data won't be clean. Use our SPF checker and DKIM lookup on each domain individually before you draw any conclusions.

Run a controlled seed test if you need cross-provider data. Postmaster Tools only shows Gmail. If you want to know how Outlook, Yahoo Mail, and others are treating each domain, a seed list service sends identical content from each domain to a panel of test addresses across providers. Tools like Mailtrap offer inbox placement testing you can run per sending domain. The key is using identical content and identical send conditions so the only variable is the domain itself.

One thing to watch: don't test too many things at once. If you change content, IP, and domain all at the same time, you won't know which variable caused the result. Change one thing, measure, then move on.

Still if you're not sure what your results are telling you, our SOS hotline is free and we're happy to look at it with you.