No listing returned
The source completed the query and returned no current listing. Other public, private or provider-specific datasets may still differ.
Check an IP against public blocklists
See whether a sending IPv4 address is currently returned by the public reputation lists queried by this tool.
- No account required
- Named sources shown
- Unavailable lookups stay inconclusive
What is an IP blocklist?
An IP blocklist is a reputation dataset of network addresses associated with spam, compromised systems, malware, open relays, missing reverse DNS or other policy concerns. Receiving mail systems may use one or more lists as signals when deciding whether to accept, reject, defer or filter a connection.
A listing does not always mean the IP directly sent spam. Some lists describe dynamic consumer ranges or addresses that should not deliver mail directly; others focus on confirmed abusive traffic. Shared cloud or hosting infrastructure can also create reputation dependencies between customers.
This tool checks the submitted IPv4 address against the named public DNS blocklists displayed in the results. It is deliberately conservative: a resolver failure or blocked query is inconclusive, not clean. The result is a snapshot and cannot predict inbox placement.
How the checker works
- 01
Validate the IPv4 address
Each octet is checked before any external reputation query is made.
- 02
Reverse the address
DNS blocklists conventionally query an IP in reverse-octet order, such as 4.3.2.1.list.example.
- 03
Query named lists
Each source is checked separately so the result remains attributable to its operator.
- 04
Classify the response
Positive, negative and unavailable answers are presented without merging uncertainty into a misleading overall score.
What IP blocklist results mean
Listed
The source returned a positive DNSBL answer. Review the operator’s category and evidence before deciding whether the IP is unsafe for mail.
Lookup unavailable
The query was refused, blocked or interrupted. This status says nothing about whether the IP is listed.
Policy listing
Some lists identify addresses that should not send mail directly rather than addresses observed sending abuse. Route mail through the authorized provider when appropriate.
What to do when an IP is listed
Identify the responsible system
Confirm the address is currently assigned to your mail server and is the IP recipients actually see. NAT, relays and provider pools can change the sending address.
Stop abusive traffic
Check queues, authentication logs, account activity, scripts and web forms. Suspend compromised credentials and contain unexpected sending before requesting removal.
Verify mail-server identity
Use stable forward and reverse DNS, a meaningful SMTP hostname, correct HELO behavior, aligned authentication and encrypted transport.
Request delisting carefully
Use the list operator’s official procedure only after fixing the cause. Repeated requests without remediation can delay or prevent removal.
Frequently asked questions
Practical answers about this checker and the signal it evaluates.
Will changing IP addresses fix delivery?+
Not reliably. Moving without correcting compromised accounts, poor list hygiene or authentication problems transfers the behavior and may damage the new address. Diagnose the cause first.
Why is a new or unused IP listed?+
It may belong to a range classified by policy, have history from a previous assignee, lack appropriate reverse DNS or share reputation with provider infrastructure. Read the source-specific reason.
Does this checker support IPv6?+
The current public checker validates IPv4 addresses because the queried sources and response conventions used here are IPv4-oriented. Do not convert or truncate an IPv6 address to force a lookup.
How long does IP delisting take?+
It varies by operator. Some entries expire automatically after abusive traffic stops; others require evidence and a manual request. DNS caches can also show an older answer until TTL expiry.