PTR record (reverse DNS)
A PTR record maps an IP address back to a hostname, which is the reverse of an ordinary lookup. Receiving mail servers check it on the connecting address, and many refuse or penalise mail from an address with no reverse name, or one whose forward lookup does not return to the same address. It is configured by whoever owns the address block.
At a glance
- Category
- DNS
- Maps
- An IP address to a hostname — the reverse of an A record
- Lives in
- The in-addr.arpa or ip6.arpa zone for the address
- Set by
- The owner of the address block, not the domain owner
- Should match
- A forward lookup that returns to the same address
- Specified in
- RFC 1035
How it works
Reverse lookups live in a special zone derived from the address itself, delegated to whoever holds the address block. When a sending server connects, the receiving server can look up the connecting address there and get a hostname. Careful receivers then resolve that hostname forward again and check it returns to the same address, which is the confirmed reverse lookup. A missing record, or one that fails the round trip, is a long-standing signal of an unmanaged or compromised host.
Why it matters
It is one of the oldest and cheapest filters a receiving server can apply, and it is still widely enforced, because legitimate mail infrastructure is nearly always configured with it and opportunistic senders on rented addresses often are not. For anyone using a sending service this is handled for them. For anyone running their own outbound path it is a prerequisite: no amount of DKIM or SPF compensates for an address with no reverse name, because the check happens at connection time, before any of the message has been seen.
Example
A company runs its own outbound server on an address from its hosting provider. The provider's control panel sets the reverse name for that address to mail.example.com. The domain also publishes a forward record for mail.example.com pointing back at the same address. A receiving server that checks both finds a consistent pair and applies no penalty; before this was configured, the same messages were routinely deferred.
Common mistakes
- 01Setting the reverse name to the hosting provider's generic hostname, which tells a receiver the address is unmanaged.
- 02Configuring the reverse record but not the matching forward record, so the round-trip check still fails.
- 03Assuming the domain owner can set it, when it is always the owner of the address block who controls the zone.
- 04Moving to a new address without setting its reverse name first, so the first campaign from it is judged before anything is configured.
Related terms
Frequently asked questions
Do I need a PTR record if I use a sending service?
No. The service owns the sending addresses and configures reverse DNS on them. It matters only if you operate your own outbound mail servers.
What is a confirmed reverse lookup?
It is the round trip: the address resolves to a hostname, and that hostname resolves back to the same address. Receivers that check both are guarding against a reverse name anybody could claim.
Can one address have several PTR records?
It is possible but unhelpful. Receivers may use any of them, so the result becomes unpredictable; a single accurate record is the sound configuration.
Sources
Last updated 16 September 2026.
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