What is blocklist.de?

blocklist.de is a community-run reporting system built around fail2ban, an open-source tool that monitors server logs and reports suspicious activity. Volunteers running fail2ban on their own servers submit attack data to a shared pool, and that pool becomes the blocklist. Think of it as a neighborhood watch where each participant flags the troublemakers they spot at their own door.

The focus is mostly on network attacks like SSH brute force attempts, FTP intrusions, and web exploits. But SMTP authentication attacks get reported too, which is where email senders need to pay attention. If your sending IP shows up in those logs, some mail servers and firewalls will query bl.blocklist.de and use it to decide whether to accept your connection.

Its impact on email deliverability is relatively low compared to the heavyweights like Spamhaus. Most major mailbox providers don't rely on it directly. But certain security-focused mail gateways and smaller hosting environments do query it, so it's worth knowing about if you're troubleshooting a delivery problem that doesn't trace back to a more obvious source.

What gets you listed:

• SMTP authentication failures that look like brute force attempts
• SSH, FTP, or web attack traffic originating from your IP
• Reports from participating fail2ban community members

The key difference from spam-focused blocklists is that blocklist.de doesn't care whether you sent spam. It cares whether your IP was involved in attack behavior. That means a shared IP on a hosting provider or an ESP can end up listed because another tenant on the same server was doing something sketchy, not because of anything you did with your email campaigns.

If you need to get delisted, visit blocklist.de/en/delist.html directly. The process is self-serve.

You can check whether your sending IP appears on blocklist.de (and dozens of other lists at once) with our free blocklist checker. If you're seeing unexplained delivery failures and can't track down the cause, that's a good place to start.