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

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.