Check an IP against email blocklists (DNSBLs)
DNS & Records
DNS Lookup Every DNS record for any domain A Record Lookup IPv4 addresses for a domain AAAA Record Lookup IPv6 addresses for a domain MX Lookup Mail servers for a domain NS Lookup Authoritative name servers TXT Lookup TXT records, SPF, verification CNAME Lookup Canonical name (alias) records SOA Lookup Start of Authority record SRV Lookup Service location records CAA Lookup Which CAs may issue certificates Reverse DNS (PTR) IP address to hostname DNSSEC Check Is the domain signed and validated? DNS Health Check A full delegation & DNS report cardEmail Deliverability
SPF Check Validate your Sender Policy Framework record DMARC Check Inspect and grade your DMARC policy DKIM Check Find and validate your DKIM public key Blacklist Check Check an IP against email blocklists (DNSBLs) SMTP Test Connect to a mail server and check STARTTLS MTA-STS Check Enforced TLS policy for inbound mail BIMI Check Brand logo record for email TLS-RPT Check SMTP TLS reporting policyNetwork & Web
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WHOIS Lookup Registration data for domains, IPs and ASNsDNS-based blocklists (DNSBLs, also called RBLs) are lists of IP addresses known for sending spam. If your mail server's IP is listed, your email may be rejected or filtered. IPeek checks your IP against a curated set of widely trusted blocklists, in real time, and shows which have listed it and why.
A DNSBL works through DNS itself. To check an IP, a mail server reverses the address and queries it as a hostname under the blocklist's zone — for 198.51.100.10 against a list at example.dnsbl, it queries 10.100.51.198.example.dnsbl. A DNS answer (typically a 127.0.0.x address) means the IP is listed; no answer means it's clean. The return code often encodes the reason for listing. IPeek runs these lookups in real time across multiple trusted lists and aggregates the results.
IPs land on blocklists for concrete reasons: sending spam or high volumes of unsolicited mail, a compromised server or malware-infected machine relaying spam, a misconfigured open relay, hitting spam traps (addresses that should never receive mail), or sharing a neighborhood with bad actors on a poorly managed network. New or recently reassigned IPs sometimes inherit a prior owner's bad reputation. IPeek shows which lists flagged your IP and, where available, the reason so you can address the root cause.
Delisting starts with fixing the cause — close open relays, patch compromised machines, stop the spam source, and authenticate your mail with SPF, DKIM, and DMARC. Then visit the specific blocklist's website and submit a removal request through its delisting form; most maintain self-service tools. Some lists expire entries automatically once spam activity stops, so clean behavior over time can clear you. Requesting delisting without fixing the underlying problem usually leads to a quick relisting.
An IP is typically listed for sending spam, being a compromised or malware-infected server, running as an open relay, or hitting spam traps. Newly assigned IPs can also inherit a previous owner's bad reputation. Listings are evidence of spam-like activity from your address, so identify and fix the source before requesting removal.
First fix the root cause — close open relays, clean infected machines, stop the spam, and set up SPF, DKIM, and DMARC. Then go to the specific blocklist's website and submit its delisting request form. Many lists also expire entries automatically once activity stops. Delisting without fixing the cause usually results in a fast relisting.
They refer to the same thing. DNSBL stands for DNS-based blocklist, and RBL (Realtime Blackhole List) was the original name coined by one of the first such services. Both describe lists of IP addresses, queried over DNS, that mail servers use to reject or filter spam. The terms are used interchangeably today.
Not necessarily. Impact depends on which list flagged you and how individual receivers use it. Some major receivers reject mail outright from listed IPs, others lower your reputation or route messages to spam, and some ignore certain lists entirely. Being on a widely trusted blocklist is serious for deliverability, but effects vary by recipient and by list.
Check whenever you notice deliverability problems — bounces, spam-folder placement, or delivery delays — and periodically as routine monitoring if you run a mail server. Listings can happen suddenly after a compromise or a sending mistake, so regular checks catch issues early. IPeek runs real-time lookups across multiple trusted blocklists so you can verify your IP's status on demand.