As reported by Word to the Wise, the DNSBL at exitnodes.tor.dnsbl.sectoor.de seems to have gone extinct. Like has happened with other lists in the past, the domain now contains a wildcard DNS entry which is bad news for DNSBLs. This means that those folks who use this DNSBL to filter mail are going to get a match on every possible IP address in the world. Every possible IP address will show up as listed, even though it's not actually listed by the blocklist.
As a result, I strongly suggest that mail administrators stop using the exitnodes.tor.dnsbl.sectoor.de DNSBL immediately.
DNSBL lookup sites should stop including exitnodes.tor.dnsbl.sectoor.de in blocklist results; the information they display would be incorrect and would scare people into thinking that they are listed, when they are not.
I don't know much about this DNSBL. Based on its name, it seems to exist to allow people to block mail from servers that host TOR Exit Nodes. If you're receiving anonymized harassing mail, that might be something you'd want to block.
The Internet Archive suggests that this list has been around since at least February 7, 2005.
June 6, 2018 Update: The DNS "wildcard" entry has been removed. This should stop any false positive issues, and means that the list is no longer "listing the world." However, the blocklist is still offline, seemingly for good, and I still strongly suggest that mail admins cease use of this list immediately.
June 6, 2018 Update: The DNS "wildcard" entry has been removed. This should stop any false positive issues, and means that the list is no longer "listing the world." However, the blocklist is still offline, seemingly for good, and I still strongly suggest that mail admins cease use of this list immediately.