What’s the difference between a DNSBL, RBL, and URI blocklist?

Blocklist type differences:

DNSBL/RBL (IP blocklists):

DNS-based Blackhole List / Realtime Blackhole List

List IP addresses that send spam

Checked during SMTP connection

Affects ability to send at all

URI blocklist (domain blocklists):

List domains found in spam content

Includes domains in links, From addresses

Checked during content filtering

Can affect delivery even from clean IPs

Examples:

IP lists: Spamhaus SBL/XBL, Barracuda, Spamcop

URI lists: Spamhaus DBL, SURBL, URIBL

You can be listed on one type without the other. Check both.

Ship registration blocklists versus cargo origin blocklists. Different registries, different consequences.