What is SURBL?
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SURBL (Spam URI Realtime Blocklists) doesn't care where your email came from. It cares where your links are going. While most blocklists flag sending IPs or domains, SURBL looks at the actual URLs inside your message body. A clean sending reputation won't save you if one of your links points to a flagged domain.
That makes it a bit of a hidden threat. You could be doing everything right on the infrastructure side and still hit the spam folder because of a third-party link, an affiliate URL, or a redirect chain you didn't even know was there.
What gets a domain listed on SURBL
- Domains showing up repeatedly across spam messages
- Phishing sites and malware distribution pages
- Affiliate links commonly associated with spam campaigns
- URL shorteners or redirectors used to mask the real destination
- Newly registered domains spun up specifically to send spam
SURBL is widely used by Spamhaus-adjacent filtering tools, SpamAssassin, enterprise security gateways, and many mailbox providers. One bad link in an otherwise legitimate email can be enough to trigger a block.
How to check if a domain is listed
Head to surbl.org/surbl-analysis and query any domain you're linking to. This is worth doing before you send, especially if you're using affiliate links, redirect services, or any URL you didn't create yourself.
If you need to request removal
The removal request form is on the same page at surbl.org/surbl-analysis (scroll down to the removal section). You'll need to show that the domain is no longer connected to spam activity and has a clear, legitimate purpose. A few things to sort out before you submit
- Remove any compromised scripts or malicious pages from the domain
- Confirm spammers aren't using your domain inside redirect chains
- Check that any third-party tools or integrations aren't injecting flagged links
Response times vary. Commercial SURBL services tend to move faster than the free tier.
Still if you're not sure which of your links might be causing problems, our free Email Header Analyzer can help you dig into what's actually in your message. Or if things are breaking and you need a second pair of eyes, our SOS hotline is free to use.
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