PTR Pointer Common
Maps an IP address back to a hostname — the reverse of an A/AAAA lookup.
What it's for
A PTR (Pointer) record does the opposite of an A or AAAA record: instead of mapping a hostname to an IP address, it maps an IP address back to a hostname. This is called "reverse DNS," and it's queried by looking up a specially formatted name inside the in-addr.arpa zone (for IPv4) or ip6.arpa zone (for IPv6), rather than through a normal forward-lookup domain name.
Unlike forward DNS, you generally can't set your own PTR records for IPs you don't own the allocation for — reverse DNS zones are controlled by whoever owns the IP block (your hosting provider, cloud platform, or ISP), so setting up a PTR record almost always means going through your host's control panel rather than your own DNS provider.
Format & syntax
For an IPv4 address like 93.184.216.34, the reverse lookup name reverses the octets and appends .in-addr.arpa:
34.216.184.93.in-addr.arpa. 3600 IN PTR example.com.
For IPv6, each hex nibble of the address is reversed and appended with .ip6.arpa (much longer, since IPv6 addresses have many more nibbles):
...(reversed nibbles)....ip6.arpa. 3600 IN PTR example.com.
- Name — the reversed IP address under
in-addr.arpaorip6.arpa - Value — the hostname that IP resolves back to
A well-configured PTR setup should ideally be "forward-confirmed" — the PTR record's target hostname should itself have an A/AAAA record that resolves back to the original IP, closing the loop.
How it's used in practice
- Email deliverability — this is by far the biggest real-world reason PTR records matter. Most major mail providers (Gmail, Outlook, etc.) check that a sending mail server's IP has a valid, matching PTR record before accepting mail from it; missing or mismatched PTR records are a very common cause of legitimate mail landing in spam or being outright rejected.
- Server identification and logging — reverse DNS lookups are commonly used in server logs, network diagnostics, and abuse reporting to identify which organization or host an IP address belongs to, without needing a separate lookup service.
- Basic anti-spam/anti-abuse heuristics — some services use "missing PTR" or "PTR doesn't match forward DNS" as one signal (among many) in spam or abuse scoring.
- Diagnostics with tools like
dig -x— running a reverse lookup is a standard first troubleshooting step to identify what's actually running on a given IP, especially on unfamiliar infrastructure.
Common mistakes & gotchas
- Assuming you can set a PTR record yourself in your normal DNS provider — you usually can't. PTR records live in a reverse zone controlled by whoever owns the IP address allocation (your cloud provider, hosting company, or ISP), so this typically requires a request through their support/control panel, not your DNS zone editor.
- Missing PTR record on a mail-sending IP — a top cause of outbound mail being rejected or spam-filtered. If you're running your own mail server (rather than using a hosted provider), setting up a correct PTR record is one of the first deliverability checks to do.
- PTR and forward DNS not matching — having a PTR record that resolves to a hostname whose own A record points to a different IP than the one you started from. Many mail servers specifically check for this "forward-confirmed reverse DNS" (FCrDNS) consistency, and a mismatch can hurt deliverability even if a PTR record technically exists.
- Forgetting reverse DNS entirely on cloud VMs — many cloud providers assign a generic default PTR record (something like
ec2-x-x-x-x.compute.amazonaws.com) unless you explicitly request a custom one, which is fine for general use but insufficient for mail-sending IPs, which usually need to match your actual sending domain.
Comparison & FAQ
| Type | Purpose | Key difference from PTR |
|---|---|---|
| A / AAAA | Hostname → IP address | The forward direction; PTR is the reverse |
| MX | Where inbound mail for a domain routes to | Unrelated data, but PTR correctness on the sending IP directly affects whether that mail gets accepted |
Why can't I add a PTR record through my normal DNS provider?
PTR records live in reverse DNS zones tied to IP address ownership, not domain ownership. Whoever controls the IP block (your hosting or cloud provider) controls those reverse zones, so you request PTR changes through them, not your regular DNS dashboard.
Does every IP address need a PTR record?
Not strictly, but it matters a lot for any IP sending email — most receiving mail servers check for a valid, matching PTR record and will penalize or reject mail from IPs that don't have one.
What does "forward-confirmed reverse DNS" mean?
It means the PTR record's target hostname, when looked up normally via its A/AAAA record, resolves back to the same IP address you started the reverse lookup from — a consistency check some mail servers and security tools use as a trust signal.
How do I check what PTR record an IP has?
Use a reverse DNS lookup tool, or the dig -x <ip> / nslookup <ip> commands from the terminal, which query the appropriate in-addr.arpa or ip6.arpa zone for you automatically.