Reverse DNS Lookup

A PTR check shows which reverse DNS name is assigned to an address, and whether it matches the forward record. You can enter an IP address or a domain name in the field: for a domain, the check takes all of its addresses, and with the checkbox enabled it also takes the mail server addresses from the MX records. For each address it queries the PTR record, then queries the forward record for the name it found, and sees whether the name resolves back to the original address. It works with both IPv4 and IPv6: their reverse names live in the in-addr.arpa and ip6.arpa zones.

Why the match goes both ways

The reverse record turns an address into a name, and the forward record turns the name back into an address. The check considers everything correct if the name from the PTR leads to the very same address. Mail systems look for exactly this pair when they decide the fate of a message.

Matching the PTR against the sender's domain makes no sense. A mail host usually has its own name, such as mx.example.net, while the domain in the message is different, so a mismatch here says nothing about the server setup. If the name does not match the address, contact the holder of the reverse zone and ask them to bring the records into line.

One address can have several PTR records. The standard allows this, but the checking side picks just one name out of them all, and there is no way to know in advance which one it will get.

Who sets up the reverse record

The PTR record is set up by the owner of the address, a hosting provider or an ISP, not by the owner of the domain. You cannot add a reverse record in the domain control panel: the reverse zone of an address is delegated separately, and for IPv4 it is a zone like 216.184.93.in-addr.arpa.

The check shows who holds the reverse zone. That is who you contact for a fix, naming the address and the name you want in your request.

Hosts often give an address a default name that contains the address itself or words like pool and dynamic. Mail systems accept such names reluctantly, so for sending mail the name is changed to your own.

When a PTR record is required

The reverse record is requested by whoever accepts mail from your host. Gmail, Mail.ru and Yandex reject messages sent from an address that has no reverse record at all, or one that does not match the forward record.

A website does not need a reverse record: browsers never ask for one. Internal network addresses have no reverse records in public DNS, and that is normal.

If mail from your domain still goes to spam, check your mail servers as a whole on the MX records lookup page and your permitted senders on the SPF record check page.