Network Tool
Reverse DNS (rDNS) Lookup
Find the PTR record (hostname) for an IPv4 or IPv6 address.
This free reverse DNS lookup tool resolves a PTR record for any IPv4 or IPv6 address, showing you the hostname an administrator has associated with that IP. Queries are performed live via DNS-over-HTTPS so results reflect current DNS state rather than a cached dataset. Reverse DNS is essential for email deliverability audits, security log analysis, and network troubleshooting.
What a PTR record is and how reverse DNS works
A PTR (pointer) record maps an IP address to a hostname — the reverse of an A or AAAA record. For IPv4, the address is reversed octet-by-octet and appended to in-addr.arpa: the PTR for 198.51.100.1 lives at 1.100.51.198.in-addr.arpa. For IPv6, the address is expanded to its full 128-bit form, each nibble (4-bit hex digit) is reversed and dot-separated, and .ip6.arpa is appended. PTR records are set by the IP address owner (usually the ISP or hosting provider), not by the domain name owner — which is why not every IP has a PTR record.
Why rDNS matters for email deliverability
Receiving mail servers perform a forward-confirmed reverse DNS (FCrDNS) check: they look up the PTR for the connecting IP, then verify the resulting hostname has an A/AAAA record pointing back to the same IP. If no PTR exists, or the PTR does not resolve back to the sending IP, many servers will reject or heavily penalize the message. Major spam filtering systems (Spamhaus, Microsoft\'s SNDS, Google Postmaster) all flag missing or mismatched rDNS as a signal for poor sender reputation. Before troubleshooting email deliverability, always check that your mail server\'s egress IP has a valid, forward-confirmed PTR record.
Live DNS-over-HTTPS queries
This tool resolves PTR records in real time using DNS-over-HTTPS (DoH), typically via a public resolver. DoH encapsulates DNS queries inside HTTPS, preventing on-path observers from seeing the lookup. Because the query goes to a live recursive resolver rather than a static dataset, results reflect current DNS propagation state — including recent PTR changes that would not yet appear in cached geolocation databases. If you recently updated a PTR record, this tool will show the new value as soon as the TTL of the old record has expired and the resolver has re-queried the authoritative server.
Frequently asked questions
What is reverse DNS (rDNS) and what is a PTR record?+
Reverse DNS is the process of resolving an IP address to a hostname, using a PTR (pointer) record. For IPv4, the query is sent to the in-addr.arpa zone; for IPv6, to ip6.arpa. PTR records are configured by whoever controls the IP allocation, not the domain owner.
Why does an IP have no PTR record?+
PTR records must be configured by the IP address owner (usually an ISP or hosting provider). Many IP blocks have no PTR delegation, and even delegated blocks often have no PTR entries for individual addresses. A missing PTR is not an error — it just means no administrator has configured one.
Why does rDNS matter for email?+
Most mail servers check that the sending IP has a PTR record and that the hostname in that PTR record resolves back to the same IP (FCrDNS). A missing or mismatched PTR is a strong spam signal that will cause legitimate mail to be rejected or quarantined.
What is the in-addr.arpa zone?+
in-addr.arpa is the special DNS zone used for IPv4 reverse lookups. The IP address bytes are reversed and appended to .in-addr.arpa to form the PTR query name — for example, 1.2.3.4 becomes 4.3.2.1.in-addr.arpa. IPv6 uses ip6.arpa with each nibble reversed.
Is this lookup free and live?+
Yes — completely free, and every lookup is resolved live via DNS-over-HTTPS, not from a cached database. Results reflect current DNS state.