rDNS and PTR

rDNS means reverse DNS, and a PTR record is the DNS data that provides it. A PTR record maps an IP address back to a hostname so receiving mail servers can verify your identity. That hostname should also have an A or AAAA record pointing at the same IP. On shared hosting we set the PTR for you. On a VPS, dedicated server, or leased IP space, you ask us or the IP owner to set it. Avoid names like localhost.localdomain, which look untrustworthy to many filters.

Match the hostname, the IP, and reverse DNS

1. Choose one hostname for outbound SMTP, usually something like mail.example.com rather than only the bare domain.
2. Create an A record for that hostname on the sending IP, and add AAAA if you send over IPv6.
3. Request a PTR that matches the same hostname. Shared hosting already uses the server name. On a VPS, open a ticket with the IP and the name you want.
4. Set the mail server HELO or EHLO to that same hostname, restart the service, and send a test to a receiver that shows Authentication-Results.

dig +short -x 203.0.113.40

Replace the documentation IP with your own address when you run this check. You want the hostname you chose, not localhost or a generic name left from a previous tenant. A PTR set to example.com while HELO uses mail.example.com creates a split identity for filters. Pick one name and keep the A record, the PTR, and HELO in agreement.

Every IP that sends mail needs a PTR

If several IPs can originate SMTP, each one needs a matching PTR record. A second IPv4 address on a dedicated server still needs reverse DNS if that address sends mail. IPv6 needs the same care when your mail software sources from it. Dual-stack sending with a missing IPv6 PTR can still hurt delivery even when IPv4 looks correct. Reverse DNS is not outdated; many receivers still check it and may score failures harshly.

DNSSEC does not replace a correct PTR record. Signed forward DNS with a wrong reverse entry is still a reverse DNS problem. See DNSSEC in plain language if you were about to sign a zone and treat outbound mail as finished.

Who sets PTR records on your service

On shared hosting we handle reverse DNS for the server hostname, so you normally do not file a ticket for the default name. On VPS and dedicated servers you control the IPs, so you request the PTR through support with the address and the target hostname. For leased IP space, coordinate with us or the IP owner so reverse DNS stays aligned with the name your mail server uses.