Reverse DNS — Reverse DNS (rDNS)
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Reverse DNS (rDNS) resolves an IP address back to a domain name — the opposite direction of a DNS lookup, which maps a name to an IP. Receiving mail servers run this check during email delivery: the sender's IP must map back (through a PTR record) to the domain the message claims to be from. A lookup that returns nothing, or resolves to a generic hosting name, is treated as a spoofing signal, so a correct PTR record is a baseline requirement for trustworthy sending, alongside SPF, DKIM, and DMARC.
More detail
The check works through a PTR (pointer) record: the sending server announces its hostname, and the receiving server looks that IP up in reverse to see whether a PTR record maps it back to the announced name. Missing or mismatched PTR is a standard spoofing signal that spam filters penalize.
For a bulk-sending platform the expectation is stronger: set the PTR to your own sending domain rather than the hosting provider's default name. For email teams it layers with SPF, DKIM, and DMARC as one more authentication layer receivers check before trusting a sender's reputation.
Sık sorulan sorular
- What is a PTR record?
- A PTR record is the DNS record type that performs reverse DNS — mapping an IP address back to a hostname. In email delivery, receiving servers check it because a stolen or unmapped IP fails authentication: the PTR entry is the concrete thing a sender configures to pass the reverse-DNS check.
- Do I need reverse DNS if I already have SPF, DKIM, and DMARC?
- Yes — receivers check all of them. SPF authorizes which servers may send for a domain, DKIM signs the message, DMARC enforces policy, and reverse DNS verifies that the sending IP maps back to a real hostname. They are complementary layers, and skipping any one weakens authentication.
See also
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