IP blocklist (DNSBL) check
Check an IP against dozens of DNS blocklists (Spamhaus, SORBS, Barracuda and more).
What is a DNS blocklist?
A DNS blocklist (DNSBL) is a database of IP addresses associated with spam, malware, and open mail relays. Mail servers check incoming connections against these lists in real time. If your IP is listed, your outbound mail may be rejected or sent to spam before anyone reads it. The check is fast because it reuses the existing DNS infrastructure: the mail server just looks up a specially formatted hostname.
Why an IP gets listed
- Sending spam directly from the IP
- A compromised machine on the IP sending spam without your knowledge
- Running an open mail relay that others are exploiting
- Inheriting a bad reputation from a previous owner of the same IP
- Being on a consumer ISP range pre-listed because residential IPs are not expected to run mail servers
Listings can happen within minutes of a spam campaign starting. A listing does not necessarily mean you did something wrong.
How to get delisted
Fix the underlying problem first. Requesting removal before the spam source is gone will result in relisting, usually faster than the first time.
- Spamhaus ZEN— check spamhaus.org/lookup. Some sub-lists (XBL, CBL) auto-remove once the malware source is cleaned. SBL requires manual review.
- SpamCop— auto-expires after roughly 24 hours with no new complaints.
- Barracuda— submit at barracudacentral.org/rbl/removal-request. Usually processed within hours.
- CBL / Abuseat— automated removal at abuseat.org/lookup.cgi after cleaning the infected system.
- UCEPROTECT— Level 1 expires after 7 days of clean behaviour. Levels 2 and 3 cover entire netblocks; contact your ISP.
Shared IPs
If you send mail through shared hosting or a shared email service, the sending IP is used by many other customers. A listing on that IP affects all of them. If the IP is shared and listed, your best option is to contact your provider or switch to a dedicated sending IP.
About this tool
This checker queries 15 widely used DNSBL zones in parallel with a 3-second timeout per query. A timeout means the list's servers did not respond in time; it does not mean your IP is listed. For a definitive answer, always verify directly on the list operator's own site.