What is RBL and DNSBL

Real Time Blackhole / Real Time Blacklist / Real Time Blocklist, all known as an “RBL” in the old days used to be a dynamic list of IP addresses where spam originates from.

a RBL is a list of IP addresses where abuse is likely to originate from and is very different from a DNSBL (DNS Black List)

DNSBL is a drop list of IP addresses intended for mail servers to DROP incoming email relay from and/or where the IP number is known to not be a real email or web server sending email on the Internet.

In the old days, there were little or no distinction between RBL and DNSBL and the terms were mutually used to describe the same thing.

What is a RBL?

In 2022, email server administrators use open source and free software, like for example Apache SpamassasinTM, to set a spam score for each incoming email. Listings on certain RBL servers as a score count or number. For example, if an IP number is listed on superblock.ascams.com, the recommended score setting is between 5 and 8 out of 20.

Email server administrators sometimes score as much as 100 points, and use many RBL lookups to score incoming email.

The practical issue however is that each lookup places a time delay on the incoming email que, which is why lists like superblock are quite popular as listings are auto managed and all abusers are easily listed and removed.

The superblock list removed over 2 million entries in the 2017 year and added 3 million in 2017. Since 2017 superblock has stopped releasing and publishing full data lists. (the main reason is that abuse is an “arms race” between anti abuse and everyone. Ascams are equally hated by ESP, Multinationals, Mom & Pop operators and well, everyone, so I guess we are doing something right as everyone dislikes us equally! ­čÖé )


What is DNSBL?

a DNSBL is a DROP list. IP addresses listed on a DNSBL incoming email will be DROPPED or REJECTED as IP addresses listed on DNSBL are known to not be email servers, regularly abused and IP owners are not managing outgoing port 25 traffic.

IP numbers on DNSBL are usually trash, because they are usually listed on hundreds of services and will take years to clean. IP Numbers listed on DNSBL are therefore generally not suited for use as an email, web or any server based application.

See also dnsbl.ascams.com