In 1997, Dave Rand and Paul Vixie, well-known Internet software engineers, started keeping a list of IP addresses that had sent them spam or engaged in other behavior that they found objectionable.Word of the list quickly spread, and they started distributing it as a BGP feed for people who wanted to block all traffic from listed IP addresses at their routers. The list became known as the Real-time Blackhole List (RBL).Many network managers wanted to use the RBL to block unwanted e-mail, but weren't prepared to use a BGP feed. Rand and Vixie created a DNS-based distribution scheme that quickly became more popular than the original BGP distribution. Other people created other DNS-based blacklists either to compete with the RBL or to complement it by listing different categories of IP addresses. Although some people refer to all DNS-based blacklists as "RBLs", the term properly is used for the Mail Abuse Prevention System (MAPS) RBL, the descendant of the original list.
I suspect nostr will have something similar for relays or npubs.
Good luck getting anyone to connect to your own relay when they are using clients that have a whitelist or connect to a trusted, centralized server to read events like Primal.
Afaik, this is already the case for LNURL providers. Some clients only show zaps if the zap receipt is from a trusted LNURL provider like strike.me or stacker.news. They won’t show zap receipts from a custom domain, because they can be faked.