Reverse DNS and PTR records
Why every mail server needs a PTR that forward-confirms, and who can set it.
Updated 19 September 2026 · 1 min read
Forward DNS maps a name to an address. Reverse DNS maps an address back to a name using a PTR record in a special zone: the address 203.0.113.10 is looked up as 10.113.0.203.in-addr.arpa. IPv6 addresses use ip6.arpa with each hex digit reversed.
Forward-confirmed reverse DNS
A PTR is only convincing if the name it returns resolves back to the same address. 203.0.113.10 → mail.example.co.uk → 203.0.113.10 is forward-confirmed (FCrDNS). 203.0.113.10 → mail.example.co.uk → 198.51.100.7 is not, and receivers treat it as no PTR at all. The IP facet shows both halves.
Why mail servers care
Receiving servers use the PTR as a first, cheap identity check. Gmail, Outlook.com and Yahoo all require sending IPs to have a valid PTR; many smaller servers reject connections from addresses whose PTR looks generic (203-0-113-10.dynamic.isp.example) or is missing. A missing PTR is one of the most common reasons a freshly set-up mail server cannot deliver anywhere.
Who can set it
The organisation that holds the address block: your hosting provider, VPS provider or ISP. Most cloud and VPS panels have a "reverse DNS" field per address; hosting on someone else's shared server means asking them. You cannot set a PTR from your own domain's DNS, because the reverse zone is not yours.
What to set it to
The hostname your mail server announces in its SMTP greeting (the HELO/EHLO name), which should itself have an A/AAAA record pointing at the address. One name per address; avoid pointing several addresses at one name unless that name has all of them as A records.
Check your own domain