Resolve any IPv4 or IPv6 address back to its hostname via PTR record. Verify rDNS configuration, check mail server setup and confirm forward-confirmed reverse DNS.
A standard (forward) DNS lookup translates a hostname into an IP address — for example, resolving "example.com" to 93.184.216.34. Reverse DNS does the inverse: given an IP address, it returns the hostname associated with it. This process queries a special part of the DNS hierarchy called the .arpa zone, where PTR records are stored. Reverse DNS is the foundation of server identification in email delivery, network security logging, and abuse investigation. To look up the forward DNS records for any domain, use our DNS Lookup tool.
A PTR record (Pointer record) is the DNS record type used exclusively for reverse lookups. For IPv4 addresses, PTR records live in the in-addr.arpa zone; for IPv6, they live in the ip6.arpa zone. The IP address is reversed to form the query name — for instance, the PTR record for 8.8.8.8 is stored at 8.8.8.8.in-addr.arpa and points to "dns.google". Unlike A or CNAME records which are managed at your domain registrar or DNS host, PTR records are managed by whoever controls the IP address block — typically your ISP or hosting provider. You can see what DNS records a domain has with our DNS Lookup tool.
Forward-confirmed reverse DNS is a two-step verification. First, a reverse lookup resolves the IP to a hostname via the PTR record. Second, that hostname is queried in forward DNS to check whether it resolves back to the original IP address. If the forward lookup confirms the same IP, the PTR record is considered forward-confirmed. This matters most for email servers: Gmail, Microsoft 365, Yahoo Mail, and most enterprise anti-spam systems perform FCrDNS checks on every incoming SMTP connection. A server that passes FCrDNS is treated as significantly more trustworthy than one that does not, reducing the chance of messages landing in spam. You can verify any domain's mail server configuration using our DNS Lookup tool to check MX, SPF, and DMARC records.
PTR records must be explicitly configured by whoever controls the IP block — not by the server owner. Residential internet connections almost never come with a PTR record. Many cloud and VPS providers ship new instances without a PTR record until you configure one manually. A missing PTR record is entirely normal for most IPs, but it becomes a problem if you are running a mail server, since receiving mail systems use PTR records as one of several signals when deciding whether to accept or flag your messages. Use our WHOIS Lookup tool to identify which organisation controls an IP block and who to contact to request a PTR record.
You must configure the PTR record through whoever assigned you the IP address, not through your domain registrar. For major cloud providers like DigitalOcean, Hetzner, Vultr, or Linode, you can set the PTR record yourself from the server or networking section of your control panel. For dedicated servers and co-location, this is usually done via the provider's support portal. For IPs assigned by a business ISP, you submit a request to their technical team. The hostname you set as the PTR record should match the hostname your mail server announces in its HELO/EHLO greeting, and that hostname should forward-resolve back to your server IP via an A record in standard DNS. You can verify the A record using our DNS Lookup tool.
Missing or broken PTR records are one of the most common reasons for legitimate email being rejected or marked as spam. Major receiving servers — including Gmail, Outlook, and Yahoo — check that the sending IP has a valid PTR record and that it forward-confirms. A server that passes FCrDNS is treated as more trustworthy during the initial SMTP connection. Best practice for any mail server is to have a PTR record that matches the server's HELO/EHLO hostname, with that hostname having an A record pointing back to the server's IP. You should also check your domain's SSL certificate is valid if you are using TLS for SMTP, and verify your port 25, 465, or 587 is open and reachable.
in-addr.arpa is the special DNS zone used for IPv4 reverse lookups. The name stands for "inverse address" within the .arpa top-level domain, which is reserved for internet infrastructure. To look up the PTR record for any IPv4 address, DNS reverses the four octets and appends .in-addr.arpa — so 192.0.2.1 becomes 1.2.0.192.in-addr.arpa. This reversal exists because DNS delegation flows from left to right, while IP notation reads from most to least significant octet. IPv6 uses the equivalent ip6.arpa zone, where the 128-bit address is expanded to 32 hex nibbles, reversed, and dotted. This tool shows you the exact arpa query name it used for every lookup.
Technically yes — the DNS standard does not prohibit it. In practice, multiple PTR records for a single IP are rare and generally discouraged. Most mail servers and network tools expect exactly one PTR record, and some spam filters treat multiple PTR records as a suspicious signal. When this tool finds more than one PTR record, it lists all of them and runs an independent forward-confirmation check on each hostname. If you find unexpected PTR records for an IP, use our WHOIS Lookup to identify the IP block owner and check whether the records are legitimate.
Reverse DNS queries the DNS system for the hostname linked to an IP address via PTR records. A WHOIS lookup queries a separate registration database for administrative details about a domain or IP block — the owner, organisation, contact information, registration dates, and network allocation. The two tools answer different questions: reverse DNS tells you what hostname an IP is configured to announce, while WHOIS tells you who owns the IP range. Together they give a complete picture of any IP address. Use this tool for PTR records, then cross-reference with our WHOIS Lookup and ASN Lookup tools for network ownership details.
Yes. Once you have the IP address from a reverse DNS lookup, our IP Lookup tool shows you the ISP, organisation, geolocation, timezone, and whether the IP is associated with a mobile network, proxy, VPN, or hosting provider. You can also run a Ping Test to check whether the host is online and responsive, or use our Port Checker to test whether specific services are running and reachable on that IP.
Many ISPs and cloud providers automatically generate PTR records that encode the IP address into the hostname itself, rather than assigning a meaningful name. For example, a residential connection might return a PTR like 37-100-215-84.dynamic.isp.example.com, and a cloud instance might show ec2-54-220-100-42.eu-west-1.compute.amazonaws.com. These auto-generated PTR records confirm that reverse DNS is configured, but they do not constitute a meaningful FCrDNS pass for email delivery purposes unless the hostname also forward-resolves back to the queried IP. If you manage the IP and need a custom, meaningful PTR record, contact your hosting provider. Use our WHOIS Lookup to identify who controls the IP block.
Spam filters use reverse DNS as one layer of a multi-signal reputation system. When an email arrives, the receiving mail server looks up the PTR record of the connecting IP. If no PTR exists, if the PTR does not forward-confirm (FCrDNS fails), or if the PTR looks like a dynamically assigned residential address (patterns like pool, dhcp, dynamic, or encoded IP addresses), the message receives a higher spam score. Combined with checks of the SPF record, DKIM signature, and DMARC policy — all verifiable via our DNS Lookup tool — a failed PTR check can tip a borderline message into the spam folder or cause outright rejection. For mail servers, a clean FCrDNS pass is a non-negotiable baseline for good deliverability.
Yes, completely free with no sign-up required. Each lookup performs a live PTR record query and a forward-confirmation check in real time, so you always see the current state of an IP's reverse DNS configuration. Both IPv4 and IPv6 addresses are fully supported. For a complete network investigation, pair this tool with our WHOIS Lookup, ASN Lookup, DNS Lookup, and IP Lookup tools.