Setting reverse DNS (PTR) for your VPS — and why mail servers need it

Reverse DNS — the PTR record — is the lookup that maps an IP address back to a hostname. It's the inverse of the A/AAAA record that maps a hostname to an IP. Most internet traffic doesn't care whether a PTR is set; mail traffic cares a lot. This article covers what PTR is, why mail servers require it, and how to set one for each IP on your LYLIX VPS in about thirty seconds.

What is reverse DNS / PTR?

Forward DNS:

$ dig +short mail.example.com
198.51.100.42

Reverse DNS:

$ dig +short -x 198.51.100.42
mail.example.com.

For the two to "match" (forward-confirmed reverse DNS, or FCrDNS), the A record for the hostname must point at the same IP that the PTR record points back to. Mail servers run this check on every inbound connection.

Why mail servers care

When your VPS connects to a remote mail server to deliver a message, that server immediately checks two things about your IP:

1. Does the IP have a PTR record at all?
2. Does the PTR's hostname resolve back to the same IP?

If either check fails, you're treated with suspicion. Common consequences:

• Gmail / Outlook / Yahoo reject or spam-folder mail from IPs without matching reverse DNS. Their SMTP banner check explicitly references it.
• Postfix on the receiving side will log hostname does not resolve to address and may reject if its reject_unknown_client_hostname restriction is on.
• Spam scoring engines (SpamAssassin, Rspamd) add points for missing or mismatched rDNS.

If your VPS sends mail of any kind — even just transactional notifications from an app — setting PTR is the single highest-impact thing you can do for deliverability.

How to set PTR on a LYLIX VPS

Sign in to customer.lylix.net, open your service, and click the Reverse DNS tab. You'll see a row for every IPv4 address assigned to the VPS — your primary IPv4 plus any additional IPv4s you've ordered. (IPv6 PTR is staff-set for now — see the IPv6 section below.)

For each IP:

1. Type the hostname you want the PTR to return (e.g. mail.yourdomain.com) into the input field.
2. Click Save.

The buttons next to each row give you shortcuts:

• Hostname — fills the input with the VPS hostname (whatever you set in your service config). Useful as a default when you don't have a more specific mail hostname.
• Reset — clears any existing override and falls back to the platform default.
• Clear — empties the input so you can type something fresh.
• Save — commits the value to authoritative DNS.

The change propagates within a minute or two — sometimes faster.

Before you click Save: set the forward record first

Forward-confirmed rDNS means the forward A/AAAA record must already point at your IP. If you set PTR to mail.yourdomain.com but the A record for mail.yourdomain.com still points to your old host, FCrDNS will fail and you're back to where you started.

Order of operations:

1. In your DNS provider, add or update an A record: mail.yourdomain.com → <your-LYLIX-IP>
2. Wait for that to propagate (couple of minutes for most providers).
3. Then set the PTR in the LYLIX portal to the same hostname.

Verify it worked

From any machine with dig installed:

# Confirm PTR returns your hostname:
dig +short -x <your-IP>

# Confirm the hostname's A record points back to your IP:
dig +short mail.yourdomain.com

# Both should match — same hostname both directions.

Or from inside your VPS:

host <your-IP>
host mail.yourdomain.com

You can also use an online checker — mxtoolbox.com/SuperTool.aspx runs the FCrDNS test and shows pass/fail with explanations.

IPv6 PTR — ticket us for now

The portal's Reverse DNS tab currently manages IPv4 PTR records only. If your VPS sends mail over IPv6 (most recipient servers now reject IPv6 connections without matching rDNS more aggressively than they do IPv4), open a ticket with the IPv6 address and the hostname you want it to resolve to. We'll set it manually on the authoritative side and confirm back. Self-service IPv6 PTR management is on the roadmap.

Common gotchas

• PTR per-IP, not per-server. If you have additional IPv4 addresses on the same VPS, each needs its own PTR. The portal tab lists them all so you don't miss any.
• One PTR per IP. Unlike A records, you can't have multiple PTRs pointing at different hostnames from one IP. Pick the most relevant hostname (usually the one you send mail as).
• SPF and DMARC are separate. rDNS is the first deliverability check; it doesn't replace SPF, DKIM, or DMARC. See the mail-server prerequisites article for the full picture.
• HELO/EHLO needs to match too. Your mail software announces a hostname when it connects (the HELO string). Configure your mail server to use the same hostname that PTR points at — three things in alignment: EHLO = PTR = A record.

Anything not behaving as expected? Open a ticket with the IP and the hostname you tried to set, and we'll dig in.