What are the main types (IP, domain, URI)?
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Not all blocklists are watching the same thing. Some check where your email came from. Some check who sent it. And some check what's inside it. If you're trying to figure out why mail is getting blocked, knowing which type is flagging you changes everything about how you fix it.
IP-based blocklists track the sending server's IP address. If the IP your mail server uses shows up on one of these, emails from that IP get blocked or sent to spam, regardless of your domain or content. Spamhaus SBL and Barracuda BRBL are two of the most widely used. IP listings are common on shared hosting, where one bad neighbor can drag everyone down.
Domain-based blocklists track your sender domain. These follow you even if you switch IPs or infrastructure. Spamhaus DBL is the main one here. A domain listing is often harder to shake than an IP listing because it signals a pattern of abuse tied to your brand, not just a server.
URI blocklists check the links inside your email body. If you include a URL that points to a flagged domain, your message can get filtered even when your sending IP and domain are perfectly clean. SpamCop feeds into URI checks, and dedicated URI lists like URIBL and SURBL are checked by many spam filters. This one catches people who link to third-party domains without realizing those domains are already flagged.
Each type needs a different fix. An IP listing? You work with your host or ESP and request removal. A domain listing? You look at your sending practices and content. A URI listing? You audit every link in your templates, including tracking pixels and redirect URLs.
If you're not sure which type is affecting you right now, our free blocklist checker scans your domain and IP against the major lists so you know exactly what you're dealing with.
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