GLOSSARY · DNS BLOCKLIST, BLACKLIST
DNSBL
A DNSBL is a list of IP addresses, published through the DNS system, that an operator has marked as sources of spam or abuse. To check an address, you reverse its numbers, add the list's domain and look up the result: an answer in the 127.0.0.x range means it is listed, and no answer means it is not.
Why it matters
Mail servers and some websites consult these lists to decide whether to accept traffic. If your address, or a proxy's address, is listed, your email may be rejected or you may face extra checks. Each list has its own rules for listing and removal, and a listing on one is not a listing on all. Shared and recycled addresses are often listed because of earlier users.
In practice
Check an address before using it for email or as a proxy. If listed, read that operator's lookup page for the reason and the removal process, and do not assume the address is wrongly listed. Some lists refuse queries sent through big public resolvers, which gives an unchecked result and not a clean one. Our check asks seven public lists.
Related terms
- Reverse DNS: Reverse DNS turns an IP address back into a name, the opposite of a normal lookup.
- Datacenter proxy: A datacenter proxy runs on a server in a hosting facility, so its IP address belongs to a hosting or cloud company and not to a home or mobile provider.
- IPv4: IPv4 is the older and still most common version of the internet's addressing system.
- IP address: An IP address is a number that identifies a device or network connection on the internet, in the way a street address identifies a building.