What’s the difference between IP and domain blocklists?

Your emails are landing in spam, or not arriving at all. You check around and someone mentions you might be on a blocklist. But which kind? Because IP blocklists and domain blocklists are two different problems, and they need two different fixes.

An IP blocklist flags the sending server's address, not your brand. If the IP you're sending from has been linked to spam (whether that was you, a previous tenant on a shared IP, or a compromised machine), the IP gets listed. Every email that travels through that IP is affected, regardless of who sent it or what domain it came from. This is especially common on shared IPs, where other senders' behaviour can drag your reputation down.

A domain blocklist flags your domain name itself. That could be your sending domain (the one in your From address), a link destination inside the email body, or a tracking domain. The key difference here is that domain reputation follows you. Switch to a new IP, a new ESP, even a new sending server, and your domain reputation travels with you. You can't outrun it by changing infrastructure.

Both matter for deliverability, but they show up differently. An IP listing hits you immediately and affects everything sent from that server. A domain listing is slower-burning but harder to shake, because it's attached to your identity, not your plumbing.

Here's how to check both:

• IP blocklists: Run your sending IP through a blocklist checker. You're looking across major lists like Spamhaus, Barracuda, and Spamcop. Your ESP's dashboard often shows this too.
• Domain blocklists: Run your sending domain through the same kind of checker. Also check any domains linked inside your emails, since URI blocklists flag link destinations specifically.

If it's an IP problem and you're on a shared IP, talk to your ESP. They may move you to a different IP, or it's worth looking at a dedicated IP if your volume supports it. If it's your own dedicated IP that's listed, you'll need to submit a delisting request and fix whatever caused the listing first (spam complaints, bounces, bad list hygiene).

Now if it's a domain listing, the fix is slower and more deliberate. Clean your list, drop your complaint rate, and start building a positive sending history. Some blocklists will auto-delist once they see improved behaviour. Others require a manual request. Either way, you can't skip the underlying fix.

You can run both checks for free with our blocklist checker. And if what you find looks complicated, our SOS hotline is free. We'll help you figure out what you're actually dealing with.