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PTR / Reverse DNS Lookup — find the hostname assigned to any IP.

Given an IPv4 or IPv6 address, the reverse-DNS lookup returns the PTR record — the hostname the IP claims to belong to. Critical for mail-server reputation (Gmail, Microsoft 365, and Yahoo all reject or spam-tag mail from IPs without matching PTR), abuse investigation, and network diagnostics. Includes forward-confirmation check (FCrDNS) to verify the PTR hostname round-trips back to the same IP.

01 · TRY IT

Reverse DNS lookup

Enter an IP address (IPv4 or IPv6). The lookup queries the appropriate .arpa reverse zone and returns the PTR record.

02 · WHAT IT RETURNS

What the PTR lookup shows

PTR hostname (IP → Host)

The hostname the IP owner has published as the reverse-DNS name for the IP. Empty answer = no PTR published (common for cloud VMs at defaults).

FCrDNS check (Round-trip verified)

Follows the PTR hostname back with an A/AAAA lookup. Match = trusted (forward-confirmed reverse DNS). Mismatch = spam-tagging by many mail servers.

Generic-hostname detection (Consumer ISP flag)

Detects residential ISP patterns (Comcast, AT&T, Verizon) that indicate a consumer connection. Mail servers typically block port 25 outbound from these IPs.

IPv4 + IPv6 both supported (in-addr + ip6 arpa)

IPv4 uses `.in-addr.arpa`, IPv6 uses `.ip6.arpa`. This tool handles both — enter either format, get the appropriate reverse zone query.

Multi-PTR handling (Rare but valid)

Some IPs publish multiple PTR records — legal but rare. All are returned with the FCrDNS check applied to each.

Chain into hosting lookup (One click)

One-click into the full reverse-IP tool for neighbours, hosting provider, and blacklist reputation on the same IP.

03 · WHY IT MATTERS

When to look up PTR

  • Mail-server deliverability Missing or mismatched PTR is the #1 cause of legitimate mail landing in spam. Check every mail-sending IP has a matching PTR before enabling outbound SMTP.
  • Abuse investigation An IP scanning your network or hitting your API — reverse-DNS tells you which organisation owns it. Correlate with ASN + WHOIS for full attribution.
  • Compliance evidence SOC 2 and ISO 27001 controls around egress often require PTR consistency for outbound-connection IPs — proves you own the sending infrastructure.
  • Cloud VM setup AWS, GCP, Azure, DigitalOcean, Linode all set default PTR on new VMs — always override to your actual mail-server hostname before enabling outbound SMTP.
  • Bulk-check reputation Sending mail from an IP without PTR is a fast route to Gmail's spam folder. Verify PTR on every outbound-sending IP as part of provisioning checklists.
04 · QUESTIONS

Common questions

  • What is a PTR record? A pointer record maps an IP address to a hostname — the reverse of an A/AAAA record. Lives in special reverse-DNS zones (`in-addr.arpa` for IPv4, `ip6.arpa` for IPv6). Only the IP's owner (usually the ISP or cloud provider) can publish PTR for it.
  • How do I set PTR for my own server? You can't directly — only the IP owner can. Cloud VMs: set through the provider's console (AWS EC2 elastic IP has a reverse-DNS field, GCP has one too). Dedicated hosting: ask your provider to delegate the reverse zone to you, or file a ticket to update it.
  • What is FCrDNS? Forward-Confirmed Reverse DNS. The PTR hostname must resolve back (A/AAAA lookup) to the same IP. Mail servers use FCrDNS as a spam signal — mismatched or reverse-only PTR is a common spammer fingerprint.
  • Why is my mobile IP's PTR a random string? Residential and mobile ISPs assign generic PTR strings (`c-73-201-14-56.hsd1.ca.comcast.net`). This signals 'consumer connection' to mail servers, which typically results in outbound port 25 blocking.
  • What's the IPv6 PTR format? Each hex nibble of the IPv6 address is reversed and dot-separated in the `.ip6.arpa` zone. `2001:db8::1` becomes `1.0.0.0...0.0.0.2.8.b.d.0.1.0.0.2.ip6.arpa` — 32 nibbles.
05 · RELATED

Related IP + DNS tools

Reverse IP Lookup (Full IP recon)

PTR + neighbours + hosting provider + blacklist reputation.

IP Blacklist Checker (Reputation)

Check the IP against 130+ blacklists.

IP Lookup (Geo + ASN)

Full IP metadata — geo, ISP, ASN, organisation.

MX Record Lookup (Forward direction)

See the mail servers for a domain — pair with reverse for FCrDNS check.