IP Reputation Checker
Look up reverse DNS, ASN, organisation, and blacklist status for any IPv4 address.
What is IP reputation and why does it affect email delivery?
Every IP address that sends email carries a reputation — a composite score derived from its sending history, blacklist status, reverse DNS configuration, volume patterns, and the quality of mail it has historically delivered. Receiving mail servers, ISPs, and filtering services continuously update reputation signals and use them to decide whether incoming connections deserve to be accepted, deferred, junked, or blocked entirely.
Reputation is not just about spam history. A brand-new IP with no history is treated with suspicion by Gmail and Outlook alike. An IP on a residential or dynamic range (covered by the Spamhaus PBL) is assumed to be an end-user device rather than a legitimate mail server. An IP whose PTR record does not match its forward DNS lookup will be rejected by strict receivers before a single byte of email content is evaluated.
Reverse DNS (PTR records)
A PTR record maps an IP address to a hostname. When your mail server connects to deliver email, the receiving server performs a reverse DNS lookup on your IP. If no PTR record exists, or if the hostname in the PTR record does not resolve forward to the same IP (forward-confirmed reverse DNS, or FCrDNS), many receivers will reject or heavily penalise your mail. Your hosting provider or ISP controls PTR records — they must be set by the IP block owner, not in your domain's DNS zone.
ASN and network reputation
An Autonomous System Number (ASN) identifies a network operated by a single organisation. Your IP's ASN matters because reputation signals are partly aggregated at the network level. If you share an ASN with a large number of known spam sources, some filters apply guilt by association. Dedicated IP addresses on reputable hosting providers with clean ASN histories consistently outperform shared IPs on commodity VPS networks.
Warming up a new IP
Never begin sending high volumes from a new IP immediately. Start with 50–100 messages per day to your most engaged recipients and increase daily volume by 2–3× each week. This establishes a positive reputation baseline with Gmail Postmaster Tools and Microsoft SNDS before you scale. Skipping warmup is one of the most common causes of sudden inbox placement collapse.
Frequently asked questions
My IP has no PTR record. How do I fix it?
Contact your hosting provider or ISP — they control reverse DNS for your IP block. Provide the hostname you want mapped (e.g. mail.yourdomain.com). The hostname must also resolve forward to the same IP.
What is a good sending IP setup?
Use a dedicated static IP (not shared or dynamic), set a matching PTR record, configure SPF to include that IP, sign with DKIM, and publish a DMARC policy. Warm the IP gradually before sending at full volume.
My IP is listed — do I need a new IP?
Usually not. Fix the root cause and delist via the link shown in results. Getting a new IP without fixing the underlying issue just moves the problem — you will be re-listed quickly.
Does this tool check IPv6?
Currently IPv4 only. IPv6 blacklist infrastructure is less standardised and DNSBL coverage is inconsistent across providers.