Blacklist Check
Check an IP or host against ~30 DNS blacklists.
Enter a value above to run Blacklist Check
e.g. 1.2.3.4
Quick answer
Blacklist Check tells you whether an IP or host is listed on about 30 DNS-based blacklists (DNSBLs) used to flag spam and abuse sources. Any "listed" result can cause your mail to be blocked or sent to spam, so aim for zero listings.
The Blacklist Check queries an IP address or hostname against roughly 30 well-known DNSBLs (DNS-based blocklists) such as Spamhaus, SORBS, Barracuda and SpamCop in a single pass. Mail servers and firewalls consult these lists to decide whether to accept, defer or reject incoming connections. If your sending IP is listed, your legitimate email may be bounced or dropped silently. This check tells you which lists flag you and which consider you clean, so you can act before deliverability suffers.
How it works
Each DNSBL is queried with a specially formatted DNS lookup: the tool reverses the octets of your IP (1.2.3.4 becomes 4.3.2.1) and appends the blocklist's zone, for example 4.3.2.1.zen.spamhaus.org. If the list holds a record for that IP, the query returns an A record in the 127.0.0.x range, meaning listed. NXDOMAIN means not listed. Roughly 30 zones are queried, so results reflect many independent operators, not one authority.
How to read the results
A clean row means that provider does not currently list you. A listed row usually includes a 127.0.0.x return code that encodes the reason, plus a link to that provider's removal page. Not every listing is equal: Spamhaus ZEN and Barracuda carry real weight with receivers, while some smaller or policy-based lists (like dynamic-IP ranges) rarely cause rejections. Focus first on the lists your recipients actually use.
Common problems & fixes
If you appear on Spamhaus, check for compromised accounts, open relays or a misconfigured web form sending spam, then request delisting after fixing the source. PBL or dynamic-range listings mean you are sending directly from a residential or dynamic IP; route mail through your provider's smart host instead. Always fix the underlying cause first, because re-listing is automatic and fast if the abusive traffic continues.
Frequently asked questions
- Should I check my IP or my hostname?
- Check the public IP that your mail server actually sends from, which is the address recipients see in the connection. A hostname is resolved to its IP first, but a domain can point to several IPs, so query the specific sending IP directly. For inbound filtering questions, also check any IPs listed in your MX records.
- I fixed the problem, so why am I still listed?
- Most blocklists do not delist automatically the moment abuse stops. Some expire after a quiet period of hours or days, while others require you to submit a removal request on the provider's site. Do not request delisting until the root cause is fixed, since a quick re-listing can lengthen future timeouts on some services.
- Does being on one list block my email everywhere?
- No. Each receiving mail server chooses which DNSBLs it consults, so a single listing affects only recipients who use that specific list. However, widely trusted lists like Spamhaus ZEN are used by a huge share of servers, so a listing there has broad impact. A minor niche listing may cause no visible problems at all.