What is a DNSBL?
A DNS-based blacklist (DNSBL), also called an RBL, is a published list of IP addresses that have been seen sending spam or other abuse. Mail servers query these lists in real time and may reject or flag email from a listed address. If your messages are bouncing or going to spam, a listing is a common cause.
Why an IP gets listed
Common reasons include a compromised device on the network sending spam, a misconfigured mail server, or simply inheriting a "dirty" address from a previous owner. Most lists publish removal (delisting) instructions once the underlying problem is fixed.
How this works
This tool runs on our server, which reverses the IP you enter and queries each blocklist's DNS zone. A response means "listed"; no record means "clean". We only send the address you provide and store nothing.