Reverse DNS (rDNS, also called a PTR record) maps an IP address back to a hostname. It is the opposite direction of a normal DNS lookup. Mail servers check it on every delivery, and on a D4 VPS you can set it yourself in one minute.
1. Know your starting point
Every VPS comes with an auto-generated hostname under d4.network. The reverse DNS of both the IPv4 and the IPv6 address is set to that hostname automatically. This default is fine for a web or app server. Change it when you want your own domain in the record, and always change it before you run a mail server.
2. Point forward DNS at your server first
Reverse DNS is only trusted when it matches forward DNS. This means the hostname in your PTR record must point back to the same IP (this is called forward-confirmed rDNS). So first, create these records at your DNS provider:
mail.example.com A 203.0.113.10 mail.example.com AAAA 2001:db8:1:2::1
Use your server's real addresses. Both are shown at the top of your service page.
3. Open the networking panel
In the client area, go to Services, open your service, and click Log In To Panel under Service actions. In the control panel that opens, pick your server and go to the Networking tab. It lists your public addresses with their current reverse DNS.
4. Set reverse DNS on IPv4
Click the edit icon at the end of the IPv4 row. The Edit Reverse DNS entry dialog shows the IP and one Reverse DNS field. Enter the hostname you created in step 2, exactly as it appears in forward DNS, and save.
5. Set reverse DNS on IPv6
Your IPv6 block is listed as a /64 with its own entries. Open the row and click the plus button to open Add Reverse DNS. Enter the exact IPv6 address the record is for (for a mail server, the address your mail service sends from) and the same hostname, then save. You can add one entry per address, and you can remove an entry with the trash icon.
The names must match exactly
Mail providers verify the full loop: IP resolves to hostname, hostname resolves to the same IP. A typo or a missing AAAA record breaks the loop. Setting rDNS on a different IPv6 address than the one your mail server sends from also breaks it. Large providers will then refuse your mail or mark it as spam, so set rDNS on the exact addresses you use.
6. Verify the loop
$ dig -x 203.0.113.10 +short $ dig -x 2001:db8:1:2::1 +short $ dig mail.example.com A +short $ dig mail.example.com AAAA +short
The first two commands should print your hostname. The last two should print the matching addresses. Changes apply fast, but DNS resolvers cache old answers for a while. Wait a few minutes and check again before you assume it failed.
Quick reference
| Task | Where |
|---|---|
| See current rDNS | Log In To Panel, your server, Networking |
| Change IPv4 rDNS | Edit icon on the IPv4 row |
| Add IPv6 rDNS | Expand the /64, plus button, pick address |
| Forward records | A and AAAA at your DNS provider |
| Verify | dig -x <ip> +short from your machine |
Where to go next
With forward-confirmed rDNS in place, you have the base for a mail server. SPF, DKIM, and DMARC records are the next layer. On any other server, a correct PTR makes your server easy to identify in logs and traceroutes.