These three tags should be merged

• rbl (30) a.k.a Real-time Blackhole List
• dnsbl (5) a.k.a. DNS-based Blackhole List
• dnsrbl (3) a.k.a. DNS-based Real-time Blackhole List

RBL and DNSBL was interchangeable each other. DNSRBL was a combination between those two.

Still I'm unsure which tag should be synonym to the other. Based on question tagged, RBL was more popular than DNSBL, although DNSBL should be seen as a more accurate technical term.