Definition
A reverse DNS record, also called a PTR (pointer) record, maps an IP address back to a hostname, the inverse of a standard forward DNS lookup that maps a hostname to an IP address. For email, a PTR record tells a receiving server what hostname an incoming connection's IP address claims to be. A valid, matching reverse DNS record is a baseline expectation for any server that sends email.
How It Works
Normal DNS resolution looks up a name such as mail.example.com and returns an IP address. A PTR record lives in the special in-addr.arpa zone (for IPv4) or ip6.arpa zone (for IPv6) and performs the reverse lookup. When a receiving server accepts an SMTP connection, it performs a reverse lookup on the connecting IP and then often verifies that the returned hostname resolves forward to the same IP.
This round-trip check is known as Forward-Confirmed Reverse DNS (FCrDNS) and is a standard part of spam filtering:
- The receiving server records the sending IP address.
- It queries the PTR record for that IP to learn the hostname.
- It then looks up that hostname's A record to confirm it maps back to the original IP.
- If the records match, the connection is more likely to be legitimate.
A mismatch, a missing PTR record, or a generic PTR assigned by a hosting provider frequently raises the message's spam filter score.
Why It Matters for Deliverability
Mailbox providers use reverse DNS as a signal of whether a sender controls legitimate infrastructure. Servers sending from dynamically assigned residential or cloud IP ranges without a proper PTR record are treated with suspicion. Establishing a correct reverse DNS record is one of the earliest steps in an email warmup or IP warming plan.
Note that the PTR record must be created by the owner of the IP address, typically the hosting provider or internet service provider, not the domain owner. A business sending from a dedicated IP should ask its provider to set the PTR record to match a hostname the business controls.
Example
A SaaS company leases a dedicated IP 198.51.100.25 for its transactional email. Its provider sets the PTR record to mail.saas.com, and the A record for mail.saas.com resolves back to 198.51.100.25. Receiving servers now see a consistent FCrDNS result, removing a common cause of delivery to spam.
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Related Glossary Terms
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Email Authentication Protocols
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Frequently Asked Questions
The owner of the IP address — usually the hosting provider or internet service provider — must create the PTR record. Domain owners can request it but cannot publish it themselves through their own DNS provider.
Forward-Confirmed Reverse DNS (FCrDNS) is the verification that a PTR record's hostname resolves forward to the same IP address that originated the connection. Receiving servers use this check to confirm the reverse DNS record is genuine.
For any meaningful sending, yes. Without a valid PTR record, many mailbox providers will reject or heavily filter your mail. It is a core component of email authentication-adjacent infrastructure and of a healthy sender reputation.