Definition
RBL
A DNS-based blocklist queried in realtime while mail is handled (Realtime Blackhole List).
In detail
RBL is an older term for DNS-based blocklists that mail systems query in realtime. You look up a reversed IP (or sometimes a domain) in a special DNS zone; a positive answer means “listed.”
Operators use RBLs with different policies: some reject, some only score. Being listed is a symptom. Fix the cause (spam, open relay, compromised host), then request delisting per the list's process.
If delivery fails with blocklist language in the bounce, identify which list and which IP. Reloop deliverability tooling helps you watch reputation signals around those incidents.
In Reloop
How RBL shows up when you use Reloop, hosted or self-hosted.
Related
Nearby terms
Other words that often show up next to RBL.
Ready to reach the inbox?
Built-in SPF/DKIM/DMARC setup, IP warming guidance, and real-time deliverability signals.