Frequently asked questions

A DNS-based blocklist (also RBL) is a list of IP addresses or domains published through DNS. A mail server asks the list about a sender; an answer in 127.0.0.0/8 means "listed", NXDOMAIN means "not listed". Each list has its own policy, so being on one list does not mean being on all.

Listed means the list has an entry for the target. Blocked means the list refused our query (for example with 127.255.255.254) and gave no verdict. It is not a listing and says nothing about your address. Some lists, such as Spamhaus, restrict queries from public resolvers; see their fair use policy. We route those lists through a relay when available.

Level 1 lists single IP addresses. Level 2 lists whole allocations (subnets) and Level 3 whole ASNs, so a listing can be caused by neighbours. UCEPROTECT itself advises complaining to your provider for L2/L3 listings (removal policy). We show them as collateral and do not count them in the verdict.

No. The Policy Blocklist contains end-user address ranges that should not send mail directly to other servers; per Spamhaus, the IPs in it are not necessarily "bad" (PBL). The usual fix is sending through your provider's authenticated SMTP submission (port 587 or 465).

First fix the cause (compromised host, open relay, missing reverse DNS). Then use the list operator's own process. Official pages we verified: Spamhaus check.spamhaus.org (handles PBL removals), Barracuda removal request, UCEPROTECT removal policy, and Microsoft sender.office.com. For any other list, contact the list operator. We cannot delist anything.

Many providers use private reputation systems with no public list. Microsoft (Outlook, Office 365) has no public DNSBL, so it cannot be checked over DNS. Also check SPF, DKIM, DMARC and reverse DNS (FCrDNS).

No. No accounts, cookies, stored IP addresses or checked targets. We keep only anonymous aggregate counters. Results are cached for up to 15 minutes to save DNS queries.

Each check sends dozens of DNS queries to third-party lists. Turnstile is a privacy-friendly bot check that keeps automated abuse from loading those lists. It applies to the web form only; the API and MCP are key-less and bounded by cache and limits.

6 checks per minute per client IP (cache hits are free), max 8 IPs and 5 MX hosts per check, 4 s per DNS query. Exceeding it returns HTTP 429 with Retry-After: 60. Full table: Docs, Limits.

For a domain, "Also check MX servers" resolves its mail servers and checks their IP addresses and names too. Use it for mail delivery problems, since MX hosts often differ from the web server.

Partly. IPv6 targets get reverse DNS and FCrDNS, but the selected IP blocklists are queried for IPv4 only. Domain lists work for any domain.

Results are cached for up to 15 minutes. After that a new check queries the lists live. List operators update at their own pace, and a delisting can take time to propagate.

MultiRBL is a small independent project run by Wojtek. It is not affiliated with any blocklist operator or with Microsoft. See also the documentation.