[ IP to Hostname | PTR Record Resolution | Mail Server Verification ]
Enter any IPv4 or IPv6 address
What is Reverse DNS?
Maps IP addresses back to domain names using PTR records.
Common Uses:
Email server verification, network troubleshooting, identifying hosts.
Example:
8.8.8.8 → dns.google
What is Reverse DNS? Reverse DNS (rDNS) translates an IP address back to a hostname using PTR (pointer) records. It's the opposite of regular DNS lookups, which convert hostnames to IP addresses. While forward DNS (A/AAAA records) is controlled by domain owners, reverse DNS is controlled by IP address owners (typically ISPs, hosting providers, or organizations with their own IP blocks).
How Reverse DNS Works: When you query an IP address like 8.8.8.8, the DNS system reverses the IP octets (becomes 8.8.8.8.in-addr.arpa) and looks up the PTR record in the special .in-addr.arpa zone. The IP address owner (in this case, Google) controls these PTR records through their authoritative DNS servers. For IPv6, the .ip6.arpa zone serves the same purpose.
Common Uses: Mail server verification (prevents spam blocking - most major email providers check PTR records), network diagnostics (identifying the purpose or owner of an IP), server owner identification (understanding who operates infrastructure), security investigations (tracking abuse sources), troubleshooting email delivery issues (SPF, DKIM, and DMARC work better with proper rDNS), and logging/monitoring (converting IP addresses to meaningful names in logs).
Why it matters: Many mail servers reject emails from IPs without proper reverse DNS records. ISPs and email providers use rDNS to verify sender legitimacy - if your mail server's IP doesn't have a PTR record pointing to your mail server's hostname, major providers like Gmail, Outlook, and Yahoo may mark your emails as spam or reject them entirely. Proper rDNS setup is considered a basic email deliverability requirement.
Email Server Best Practices: For mail servers, your forward DNS (A record for mail.example.com pointing to 1.2.3.4) should match your reverse DNS (PTR record for 1.2.3.4 pointing to mail.example.com). This matching is called forward-confirmed reverse DNS (FCrDNS). Many spam filters award higher reputation scores to mail servers with proper FCrDNS alignment. Without it, expect 30-50% delivery rate to major providers.
Common PTR Record Patterns: ISPs often assign generic PTR records like "123-45-67-89.isp.com" for residential connections. Hosting providers typically use patterns like "server1234.datacenter.hosting.com". Dedicated servers and cloud instances usually allow custom PTR configuration through control panels. Understanding these patterns helps identify connection types (residential, datacenter, cloud) during security analysis.
Limitations and Troubleshooting: Not every IP has a PTR record - this is normal for consumer/residential connections. Some hosting providers may take 24-72 hours to update PTR records after you request changes. Remember that you can only set PTR records for IP addresses you own or control through your hosting provider; you cannot set PTR records from your domain's DNS zone.
Related tools: DNS Lookup · WHOIS Lookup · IP Geolocation · SSL Checker
What does reverse DNS return? It returns a hostname (PTR record) associated with an IP address. For example, querying 8.8.8.8 returns "dns.google" while 1.1.1.1 returns "one.one.one.one". Many hosting providers return hostnames under their domain like "server123.hosting.com" or geographic indicators like "us-east-1.cloud.example.net".
Is missing reverse DNS always a problem? Not for normal browsing, downloading, or most online activities. It matters most for email sending (IP reputation requirements), some security tooling (verification processes), server identification (understanding network ownership), and meeting compliance requirements. Residential ISP connections typically don't need PTR records, but mail servers absolutely do.
Why can't I set PTR records in my domain DNS? PTR records live under the special .in-addr.arpa reverse zones controlled by the IP owner, not your domain registrar. You need the ISP/cloud provider to set it. Think of it this way: your domain DNS controls "what IP addresses your domain points to" while reverse DNS controls "what hostname an IP address identifies as." These are managed by different authorities to prevent abuse.
How do I set up reverse DNS for my mail server? Contact your hosting provider, cloud platform (AWS, Azure, GCP), or ISP and request PTR record configuration. Provide your mail server's hostname (e.g., mail.example.com) and the IP address. Most providers offer self-service PTR management in control panels. For cloud platforms: AWS Route 53 (request via support), Azure DNS, Google Cloud DNS allow PTR management. Verify changes with this tool after 1-6 hours.
What if my PTR record doesn't match my hostname? This mismatch causes email deliverability issues. If your server identifies as "mail.example.com" but PTR shows "vps12345.hosting.com", receiving servers flag this inconsistency. Update your PTR to match your HELO/EHLO hostname. Some administrators set up the reverse: configure HELO to match the existing PTR, though the first approach is preferred.
Can one IP have multiple PTR records? Technically possible but strongly discouraged. DNS standards recommend one PTR record per IP. Multiple PTR records cause unpredictable results as queries may return different values. For hosting multiple domains on one IP, use a single PTR record pointing to the primary hostname, and ensure TLS/SNI handles the multiple domains properly.
What should I check next? Use DNS Lookup for forward records (A, AAAA, MX, TXT), WHOIS to understand ownership/registration details, and SSL Checker to verify certificate configuration. For complete mail server setup, also verify SPF, DKIM, and DMARC records using DNS Lookup.