RBLs (blocklists) flag IPs or domains associated with spam. Learn how RBLs work, how checks are done, and what to do if you’re listed.
An RBL (Realtime Blackhole List) is a type of blocklist used to identify IP addresses or domains suspected of sending spam or abusive email. Mail servers can query these lists during delivery to decide whether to accept, reject, or filter a message.
Many RBLs are DNS-based (DNSBL), meaning the lookup is done via DNS queries. Results can vary by list because each one has different listing criteria and delisting procedures.
If you’re listed, the first step is stopping the cause: compromised accounts, bad lists, or sudden volume spikes. Then follow the specific delisting process and improve ongoing hygiene so you don’t get relisted.