Guide
Reverse DNS (RDNS) — Common searches and answers
Reverse DNS (rDNS) shows which name an IP maps back to via PTR. Mail servers dump messages to spam if PTR is missing or does not match the A record. This page answers “what is a PTR”, “how to check rDNS” and “what domain is this IP”. Query only your own IP or an authorised range.
Why PTR affects mail
The receiving host compares HELO/EHLO, the connecting IP and PTR. No name, or a random hosting label, looks low-trust. Correct setup: A record mail.example.com → IP, PTR on that IP → mail.example.com. One direction is not enough.
PTR is written by the IP owner (server or datacentre), not the domain registrar. On VDS or corporate mail you open a ticket: “set PTR to …”. On shared hosting PTR usually belongs to the provider and will not change.
How to read the result
A filled PTR shows the name. Empty means no record and higher mail risk. If the name does not match the A record, forward-confirmed reverse DNS is broken. Multiple PTRs on one IP are a bad idea; the receiver picks one at random.
On IPv6, PTR lives under ip6.arpa. The tool tries both v4 and v6. A VPN or CGNAT egress PTR may not be your brand; corporate sending needs a stable egress and your own PTR.
Security and permission
Do not scan someone else’s IP block. PTR is public but bulk scanning is unauthorised reconnaissance. Webify accepts one IP. The result is a name lookup, not an open-port scan.
Setup, search and common traps
Searches: “what is rDNS”, “how to add PTR”, “IP to domain”, “mail spam PTR”. Order: lock A/AAAA first, then ask the datacentre for PTR, then verify here after 24 hours. Trap: setting a hostname in the panel and assuming PTR appears. Most VDS boxes need a ticket. Second trap: a www PTR; mail wants mail. or mx.
An RBL check is not PTR; it is a separate list. Even with a correct PTR, a listed IP still drops mail. The reverse happens too: list is clean, PTR is missing, Gmail still files spam. Diagnosis has three legs: A, PTR, list. This page shows only the second. Corporate sending needs a stable egress IP and a branded PTR on that IP; shared SMTP does not give you that.