What is Backscatterer?
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Imagine a spammer forges your domain as the "from" address on thousands of messages. Those messages hit mail servers that accept them, then realize they're junk, and bounce them back to you. You never sent anything. But now your inbox is flooded with delivery failure notices, and the server that bounced them just got flagged. That's backscatter.
Backscatterer (ips.backscatterer.org) is a blocklist that targets the servers doing the bouncing, not the spammer. It lists IPs that generate backscatter: those unsolicited bounce messages (also called NDRs) sent to forged addresses. The server didn't cause the spam, but it made the problem worse by creating collateral noise for innocent people.
The fix for mail server operators is straightforward in principle. Reject suspicious messages during the SMTP connection, before accepting them. If you accept a message and then decide to bounce it later, you're sending that bounce to whoever's address was forged. That person never asked for it. Accept-then-bounce is the pattern Backscatterer specifically targets.
Auto-responders with the same problem get listed too. If your out-of-office reply fires back at a forged address, you're creating the same issue.
There are two different situations here worth separating out:
- If your IP is listed: Your mail server is bouncing messages instead of rejecting them at SMTP time (or an auto-responder is misconfigured). Fix the configuration first, then request delisting at backscatterer.org.
- If your domain was spoofed: You're the victim, not the listed party. The servers that accepted and bounced those forged messages are the ones getting flagged. This is one of the reasons a solid DMARC policy matters. It tells receiving servers to reject or quarantine messages that fail authentication, rather than accepting and bouncing them.
Backscatterer has a relatively low impact compared to lists like Spamhaus. Not every receiver queries it. But if your server's behavior is generating backscatter, that's worth fixing regardless of whether you're listed anywhere.
Not sure if your IP is on any blocklists right now? Check with our free Blocklist Checker. And if your mail server config is the issue and you're not sure where to start, our SOS hotline is free.
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