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Configure reverse DNS

3 min read07 November 2026

Reverse DNS maps an IP address to a name. It does not make a website work, but it weighs heavily on mail server reputation. A missing or inconsistent PTR gets your messages filed as spam, even with correct SPF and DKIM.

What a PTR record is

A PTR lives in a reverse zone: in-addr.arpa for IPv4, ip6.arpa for IPv6. It belongs to the address owner, not to you. You do not create it in your domain's zone.

The reference check is forward-confirmed reverse DNS (FCrDNS): the PTR gives a name, and that name must have an A or AAAA for the same address.

  • PTR: address to name.
  • A / AAAA: name to address.
  • Both must match, or reputation suffers.

Who controls the PTR

On a NeoHeberg VPS, public IPv6 is included and dedicated IPv4 is optional. The PTR belongs to the address, so NeoHeberg publishes it. If the option appears in the VPS panel, use it; otherwise open a ticket with the address and the desired name.

On web hosting you do not control the address: the PTR belongs to the provider and cannot be customised. Use the platform's SMTP servers instead of sending directly from a PHP script.

Do not expect a DNS zone change to alter a PTR: it does not touch the provider's reverse zone.

Align mail and PTR

Pick a stable name, for example mail.your-domain.com, and create its A and AAAA before requesting the PTR.

The mail server must announce the same name in its SMTP banner (HELO/EHLO). With Postfix, that is myhostname:

Text
myhostname = mail.your-domain.com

A correct PTR with a different HELO creates a mismatch. The useful trio remains: consistent PTR, valid SPF, signed DKIM. Add DMARC in observation mode to receive reports.

If you send over IPv6, request a PTR for the IPv6 address too. Many receivers are stricter about IPv6 without PTR than about IPv4, because the space is huge.

Verify

Replace the values with your real addresses:

Bash
dig -x YOUR_IPV4 +short
dig -x YOUR_IPV6 +short
dig +short A mail.your-domain.com
dig +short AAAA mail.your-domain.com

The last two must return the address used by the PTR. Then send a real message to an external mailbox and read the received headers: hostname and address must agree.

A PTR change is usually visible quickly, since the reverse zone often has a short TTL. If the old name persists, check with a public resolver before requesting another change.

Common mistakes

  • PTR left at the provider's default name, unrelated to the domain.
  • Correct PTR but the name is missing from the zone: the forward check fails.
  • Sending over IPv6 without an IPv6 PTR.
  • Changing IP address without a new request: the old PTR does not follow.
  • Expecting a custom PTR on web hosting, where the address belongs to the provider.

Reverse DNS replaces neither SPF, DKIM nor DMARC. It removes a technical doubt; reputation also depends on content, complaints and regularity.

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