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MultiRBL Check

Available

Check an IP address or mail server hostname against multiple DNS-based blacklists to identify potential email-delivery problems.

Check blocklists

Public IPv4 or IPv6 address, or a mail server hostname. Hostnames are checked on domain lists directly and on IP lists through their addresses.

Blocklists

How it works

For each selected blocklist the server builds the provider’s query name (reversed IPv4 octets, reversed IPv6 nibbles or the hostname) and queries its DNS zone. An answer inside 127.0.0.0/8 means listed, NXDOMAIN means not listed, and documented error codes, timeouts and failures are reported as such — never as clean. Hostnames are checked directly on domain lists and through their IP addresses on IP lists.

Safeguards & responsible use

  • Each provider is queried in its published format and within its usage policy, rate limits and access requirements (some require registration or an API key).
  • IPv6 and hostname queries are only sent to lists that support them; others are reported as “Unsupported query”.
  • A DNS failure or timeout is never treated as “not listed”.
  • Server-side validation, per-client rate and concurrency limits and per-query timeouts. Only blocklist zones from the configured list can be queried — no general DNS access.
  • Results are cached only where the provider’s terms allow it, and briefly.

Frequently asked questions

What is an RBL or DNSBL?

A real-time blocklist published through DNS. Mail servers query it for the connecting IP (or a domain) and may reject or score mail from listed sources.

Why is a list shown as “unavailable” instead of “not listed”?

Some lists refuse queries from public resolvers or above a quota, and some time out. In those cases the listing status is unknown, so NetTools says so rather than reporting a clean result.

My IP is listed — what should I do?

Find and fix the cause first (compromised account, open relay, missing reverse DNS, sudden volume), then follow the removal procedure linked for that list.

How is this different from Email Blacklist Check?

MultiRBL lets you choose the lists and shows per-list return codes and diagnostics. Email Blacklist Check gives a quick yes/no overview.