What is forward-confirmed reverse DNS (FCrDNS)?

A two-way check: the IP's PTR record gives a hostname, and that hostname's own A or AAAA record must resolve back to the same IP. Receivers trust FCrDNS because it cannot be forged by controlling DNS on one side alone.

Why does my mail get rejected with no PTR record?

A sending IP with no PTR, or one that fails to resolve back to itself, looks like a residential or dynamically assigned address to a receiver, which is where most spam originates. Many receivers refuse or heavily penalise it.

Who sets the PTR record?

Whoever controls the IP address, not the domain. Ask your hosting provider or cloud platform to set it; you cannot add a PTR record through your own domain's DNS.

Reverse DNS lookup

Reverse DNS maps an IP address back to a hostname through a PTR record, and most receivers check it before accepting a connection. This tool looks up the PTR record for an IP and confirms whether the hostname resolves back to the same address.

What this tool checks

The tool queries the PTR record for the IP in the in-addr.arpa (IPv4) or ip6.arpa (IPv6) reverse zone to get a hostname, then resolves that hostname's own A or AAAA record to see if it points back to the same IP. Both directions have to agree for the check to count as confirmed.

Why receivers check this

A one-sided PTR record, one that exists but does not resolve back, can be set by anyone who controls DNS for that hostname, so it proves nothing on its own. Forward confirmation requires control of both the reverse zone (the IP's owner) and the forward zone (the hostname's owner), which is normally the same party for a real mail server and rarely true for spam infrastructure.

Reverse DNS and Spamjadoo

Spamjadoo checks reverse DNS at connection time, before EHLO, as one of the facts that can end a session immediately. See how it works for where this sits in the full sequence of checks.

Questions people ask

What is forward-confirmed reverse DNS (FCrDNS)?: A two-way check: the IP's PTR record gives a hostname, and that hostname's own A or AAAA record must resolve back to the same IP. Receivers trust FCrDNS because it cannot be forged by controlling DNS on one side alone.
Why does my mail get rejected with no PTR record?: A sending IP with no PTR, or one that fails to resolve back to itself, looks like a residential or dynamically assigned address to a receiver, which is where most spam originates. Many receivers refuse or heavily penalise it.
Who sets the PTR record?: Whoever controls the IP address, not the domain. Ask your hosting provider or cloud platform to set it; you cannot add a PTR record through your own domain's DNS.