How do you tell if you have a domain-level or IP-level problem?

Your emails are hitting spam or getting blocked, and you need to know where to point the finger. Is your sending IP the problem, or has your domain itself picked up a bad reputation? The answer changes everything about how you fix it, so let's work through the diagnosis properly.

What you're actually measuring

Your domain reputation is tied to your brand. It travels with you no matter which IP or ESP you use. Your IP reputation belongs to the sending address itself. If you're on a shared IP, other senders can damage it. If you're on a dedicated IP, it's all yours.

Both can drag you into spam independently, so you need to check both before assuming you know which one is broken.

Start with the tools that just tell you

Gmail Postmaster Tools is your clearest starting point. It shows domain reputation and IP reputation as separate scores (High, Medium, Low, Bad). If your domain score is Low and your IP score is High, you know where to focus. If both are Low, you have a harder road ahead.

Outlook's Smart Network Data Services (SNDS) gives you IP-specific data from Microsoft's mail network. It won't show domain reputation, but if your IP is flagged there, that's a concrete signal.

Run an isolation test

If the tools don't give you a clean answer, run one of these tests deliberately.

• Same domain, different IP. Send from your domain through a completely different IP address (a different ESP, a different sending pool, or a fresh dedicated IP). If delivery problems follow you, the domain is the issue.
• Same IP, different domain. Send from a clean test domain through your existing IP. If that test domain lands fine, your sending IP is probably healthy and the problem sits with your main domain.

You need a clean baseline for these tests to mean anything, so send to a seed list or test accounts you control, not your full subscriber list.

Read your bounce messages

Bounce codes often tell you directly. IP-based blocks will reference a specific IP address or IP range in the rejection message. Domain-based blocks will name your domain or mention your domain's reputation. Look for the difference in the actual text, not just the error code.

Now if you're not sure how to pull and read those, our free Email Header Analyzer can help you decode what came back.

Check the blocklists for both

Some blocklists track IPs. Some track domains. Spamhaus maintains both types. Run a blocklist check against your sending IP and separately against your domain. Being on an IP-based list with a clean domain is a very different problem from having your domain on a domain-based list. Our free Blocklist Checker covers both.

What to do once you know

Now if it's an IP problem, you have more options. On a shared IP, talk to your ESP about moving to a cleaner pool or a dedicated IP. On a dedicated IP, the fix is behavioral: stop sending to unengaged contacts, reduce volume, and rebuild sending history over weeks.

If it's a domain problem, that's harder. The reputation follows your domain name, so there's no IP change that fixes it. You need to address the root cause, whether that's list quality, complaint rates, or authentication gaps, and then send consistently to your most engaged subscribers while you wait for mailbox providers to re-evaluate you. It takes time (think weeks to months, not days).

If you're not sure what you're seeing or the signals seem contradictory, that's exactly what our SOS hotline is for. No pitch, just help.