Check and fix reverse DNS (PTR) so your email is not rejected

Large mailbox providers look up the PTR record of the IP that delivers a message. If it is missing, generic, or does not match a hostname that points back to the same IP, mail goes to spam or bounces. This guide is the hands-on check-and-fix; the concept is explained in what is reverse DNS.

Before you start

• A server that sends mail directly (a VPS or dedicated server). On MdmHost shared and reseller hosting, rDNS for the server IP is already managed for you.
• A hostname you control, such as mail.example.com or server1.example.com.
• Access to the zone for that domain (Zone Editor) and to your VPS panel or support.

Find the IP your mail is sent from

Send a message to a Gmail account, open it, choose Show original and look at the first Received: from line added by Google. The IP there is your sending IP. On the server you can also check:

curl -4 ifconfig.me
curl -6 ifconfig.me

Check the current PTR

dig +short -x 203.0.113.25

A good result is a real hostname like mail.example.com.. Bad results are an empty answer or a generic name like 203-0-113-25.provider.net.

Make forward and reverse DNS match (FCrDNS)

1. Create the A record: in your DNS zone add mail.example.com → 203.0.113.25 (and an AAAA record for IPv6 if used).
2. Set the PTR: only the owner of the IP block can do this. In Virtualizor use the rDNS option (set reverse DNS in Virtualizor); otherwise open a ticket with the IP and the hostname.
3. Set the server hostname to the same name and use it as the mail server's HELO name (set hostname and reverse DNS). In WHM, the hostname is under Networking Setup → Change Hostname.

Verify

dig +short -x 203.0.113.25
dig +short mail.example.com A

The first must return mail.example.com., the second 203.0.113.25. Then test the SMTP banner:

telnet mail.example.com 25

The 220 greeting should show the same hostname. PTR changes can take a few hours to be seen everywhere because of caching.

Do not forget SPF, DKIM and DMARC

rDNS is only one part of sender trust. Publish SPF, DKIM and DMARC too: set up SPF, DKIM and DMARC in cPanel.

Troubleshooting

• Bounce says "PTR record setup" or "550 5.7.25": the IPv6 address lacks a PTR. Add one or force IPv4 for SMTP.
• PTR correct but mail still in spam: check the IP on blocklists and your authentication results in the message headers.
• Several domains on one server: a PTR holds one hostname. Use the server hostname, not each customer domain.

Next steps

• What is reverse DNS
• SPF, DKIM and DMARC in cPanel
• DNS record types explained