IP Blacklist / DNSBL Checker

Q: Why would a legitimate mail server end up on a blacklist?

Common causes include a compromised account or machine sending spam, a misconfigured mail relay accepting unauthorized mail, sending to purchased or scraped mailing lists, or inheriting a previously-abused IP on shared or cloud infrastructure.

Q: Does being blacklisted mean my mail won't be delivered at all?

It depends on the receiving server and which blacklist. Major providers use their own internal reputation systems, though smaller mail servers that explicitly subscribe to a listing blacklist will reject or quarantine based on it directly.

Check an IPv4 address against major DNS-based blacklists used by mail servers to reject or flag spam. Queries run directly from your browser to a public DNS resolver.

IPv4 Address

Live check — queries each DNSBL zone (Spamhaus, Barracuda, SpamCop, SORBS, UCEPROTECT, PSBL, Backscatterer) directly via DNS over HTTPS at request time. See the full methodology page.

How DNSBL checks actually work

A DNSBL (DNS-based Blacklist) is queried by reversing the IP's octets and appending the blacklist's zone name — for example, checking 203.0.113.10 against Spamhaus ZEN means querying 10.113.0.203.zen.spamhaus.org as a normal DNS A record. If the zone returns an answer (typically an address in the 127.0.0.x range), the IP is listed; if it returns NXDOMAIN, it isn't. This tool runs exactly that query, directly from your browser, against each blacklist below.

If your IP is listed

Each blacklist has its own delisting process — most (Spamhaus, SpamCop, Barracuda) offer a free self-service removal form once the underlying cause is fixed (open relay, compromised host, infected machine on the network, or a shared IP previously used by a spammer). UCEPROTECT is a notable exception — some of its tiers only auto-expire over time and are widely considered overly aggressive by mail administrators; many receiving servers don't actually enforce UCEPROTECT-only listings for that reason.

Shared hosting and IP reputation

If you're on shared hosting or a cloud provider's IP pool, a previous tenant's bad behavior can leave the IP listed before you ever used it. Checking on a schedule (or before going live on a new IP) catches this before it affects your mail deliverability.

Why would a legitimate mail server end up on a blacklist?

Common causes: a compromised account or machine sending spam without the owner's knowledge, a misconfigured mail relay accepting mail from unauthorized senders, sending to purchased or scraped mailing lists that generate spam complaints, or simply inheriting a previously-abused IP on shared/cloud infrastructure.

Does being blacklisted mean my mail won't be delivered at all?

Depends on the receiving server and which blacklist. Major providers (Gmail, Outlook.com) use their own internal reputation systems and don't necessarily block based on third-party DNSBLs directly, though a poor sending reputation across the board still hurts inbox placement. Smaller mail servers and spam filters that explicitly subscribe to a listing blacklist will reject or quarantine based on it directly.

Can I check a domain name instead of an IP?

Traditional DNSBLs check IP addresses, not domains — you'd need to first resolve your mail server's sending IP (its MX record's A record) and check that. A few domain-based blacklists exist (URIBL, SURBL) for checking domains referenced in email bodies, which this tool doesn't cover.