PTR What is a PTR Record?

What is a PTR record?

A PTR (Pointer) record maps an IP address to a hostname — the reverse of what an A record does. Instead of asking "what IP does this domain resolve to?", a PTR lookup asks "what hostname does this IP address belong to?" This process is called reverse DNS lookup.

PTR records live in a special reverse DNS zone. For IPv4, the convention is to reverse the IP address octets and append .in-addr.arpa.. For example, the PTR record for 93.184.216.34 lives at 34.216.184.93.in-addr.arpa..

Anatomy of a PTR record

34.216.184.93.in-addr.arpa.  3600  IN  PTR  example.com.

For IPv6, addresses are reversed nibble-by-nibble in the .ip6.arpa. zone — for example, 2001:db8::1 becomes 1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.8.b.d.0.1.0.0.2.ip6.arpa.

How to look up a PTR record

Use nslookup with the -type=PTR flag, or simply pass an IP address (nslookup does reverse lookups automatically when given an IP):

# Reverse lookup with nslookup
nslookup 93.184.216.34

# Explicit PTR lookup with dig
dig -x 93.184.216.34

# Or via the full reverse DNS name
dig 34.216.184.93.in-addr.arpa PTR

Why PTR records matter for email

Many mail servers perform a reverse DNS check on incoming connections: they look up the PTR record for the connecting IP and verify that it resolves to a hostname that matches the sending domain. This is called a forward-confirmed reverse DNS (FCrDNS) check. A missing or mismatched PTR record is a strong spam signal — mail from servers without a valid PTR record is frequently rejected or sent to spam.

If you're running a mail server, your PTR record must:

• Exist — the sending IP must have a PTR record.
• Match the hostname used in the SMTP HELO/EHLO greeting.
• Forward-resolve — the hostname in the PTR record must have an A record that points back to the same IP.

PTR records for a public IP are set by whoever controls that IP block — usually your ISP or hosting provider. You must contact them (or use their control panel) to set or update your PTR record.

Common uses

• Email deliverability — required for mail servers to pass FCrDNS checks and avoid spam filters.
• Network logging — SSH and network monitoring tools display hostnames instead of raw IPs when a PTR record exists, making logs easier to read.
• Security tooling — intrusion detection and SIEM systems use reverse DNS to enrich IP addresses with hostnames.
• CDN and cloud — cloud providers assign PTR records to their IP ranges; custom PTR records can be configured in most hosting control panels.

Common mistakes

• Trying to set PTR records at your DNS host — PTR records must be set by the owner of the IP block (your ISP or VPS provider), not in your domain's DNS zone. Your registrar's DNS has no authority over the in-addr.arpa zone.
• Mismatched forward and reverse — the PTR record must point to a hostname that A-records back to the same IP. A PTR record pointing to a different IP than the A record will fail FCrDNS checks.
• Generic PTR records — ISPs assign generic PTR records like 93-184-216-34.example-isp.net. This won't satisfy mail server checks that expect the PTR to match the sending domain. Request a custom PTR record from your provider.