Reverse DNS lets a receiver look up the name behind a sending IP address, and mail from IPs without it is often rejected.
Key points
- A PTR record for 192.0.2.10 lives at 10.2.0.192.in-addr.arpa [1]; IPv6 addresses use a similar zone under ip6.arpa.
- Forward-confirmed reverse DNS means the PTR name resolves back, through an A or AAAA DNS Record, to the original IP [2].
- Gmail requires every sender's IPs to have valid forward and reverse DNS, also called PTR records [3].
- PTR records are controlled by whoever owns the IP block, usually the hosting provider or Email Service Provider (ESP), not the domain's DNS host.
- Generic PTR names that look like home broadband ranges are a common spam signal and can hurt IP Reputation.
- Senders using a mailbox provider such as Google Workspace or Microsoft 365 get correct reverse DNS automatically, because they send from the provider's IPs.
How reverse DNS works
Normal DNS answers the question of which IP address a name points to. Reverse DNS answers the opposite: which name an IP address belongs to. The address is written backwards under a special domain, so 192.0.2.10 becomes 10.2.0.192.in-addr.arpa, and a PTR record there holds the host name [1]. RFC 1912 advises that every PTR name should also have a matching A record, and that mismatches cause problems for services that rely on reverse lookups [2]. Mail servers do exactly this check. When a server connects, the receiver looks up its PTR, then looks up the returned name to see whether it points back to the same IP. If both directions agree, the sender has forward-confirmed reverse DNS, a basic sign of a properly run server.
Why receivers check it
Much spam comes from hijacked home computers and poorly managed servers. Those machines usually have no PTR record, or a generic one that encodes the IP address and an internet provider's name. Legitimate mail servers, by contrast, have a stable name that the operator chose. That makes reverse DNS a cheap first filter, applied before any content is read. Gmail lists valid forward and reverse DNS among the requirements for all senders, not only bulk senders [3]. Missing or mismatched PTR records can cause outright rejections or a lower IP Reputation, which affects every message from that address. Addresses with generic names often sit in ranges that blocklists mark as not meant to send mail directly. The check also ties into the HELO name a server announces under SMTP, which should match its PTR.
Setting up reverse DNS
Only the owner of an IP address block can set its PTR records. For a dedicated server, that means asking the hosting or cloud provider, or using its control panel. For a shared or dedicated IP at an Email Service Provider (ESP), the provider usually handles it, sometimes with an option to use a host name on your own domain [4]. People who send from Gmail, Google Workspace or Microsoft 365 do not need to do anything: their mail leaves from the provider's servers, which already have correct forward and reverse DNS. For Cold Email sent this way, reverse DNS is rarely the problem. It becomes important when a team runs its own mail server or moves to dedicated infrastructure.
Related terms
Outreach without the busywork.
PineLead finds new B2B prospects every day, qualifies them against your criteria and writes the first email in your voice. You approve — PineLead sends.
Start free with 100 credits →