---
title: "Reverse DNS and sending identity"
description: "Every sending IP needs stable forward-confirmed reverse DNS, an SMTP greeting that matches it, and an operational domain identity."
canonical: https://specification.email/spec/deliverability/reverse-dns/
category: deliverability
status: required
sources:
  - title: "RFC 5321 — SMTP client identity"
    url: "https://www.rfc-editor.org/rfc/rfc5321#section-4.1.4"
    publisher: "IETF"
---

# Reverse DNS and sending identity

> Every sending IP needs stable forward-confirmed reverse DNS, an SMTP greeting that matches it, and an operational domain identity.

## What it is

Reverse DNS maps a sending IP to a hostname. Forward-confirmed reverse DNS means that hostname resolves back to the IP.

## Why it matters

Mailbox providers expect accountable infrastructure. Missing or generic identity is a common rejection and reputation signal.

## How to implement

Assign a dedicated, meaningful hostname to each sending IP, configure PTR through the IP owner, publish matching A or AAAA records, and use that hostname in SMTP EHLO.

## Common mistakes

- Setting a PTR that does not resolve forward.
- Sharing one hostname between unrelated operators.
- Greeting with `localhost` or a bare IP literal.

## Verification

Resolve IP → PTR → address and compare the SMTP banner and EHLO name. Repeat from a resolver outside your own network.