What is RBL?

RBL (Realtime Black Lists) are also called DNSBL (DNS-based Blackhole List) and are real-time queryable public or closed blacklists used to classify email of dubious origin as spam.

An RBL is a listing of domain names, as well as email and IP addresses, that have attracted attention for negative communications or problematic content.

There are countless RBLs, which are constantly updated by the respective owners and users.

In addition, there are also ‘RWL’, i.e. ‘Realtime White Lists’, on which secured positive Internet participants are stored and can be queried.

See also:
Wikipedia: RBL