The one-sentence version#
A PTR record maps a sending IP address back to a hostname. Mailbox providers check that the PTR resolves and that the hostname's A record points back to the same IP (forward-confirmed reverse DNS).
Why you should care#
Gmail's sender guidelines require valid forward and reverse DNS. Missing or generic PTRs are a classic spam signal and cause outright rejections at many gateways.
The mental model#
Think of reverse DNS (PTR) records as a contract between you and the mailbox providers receiving your mail. You publish or configure something they can check; they check it on every message; the result feeds their decision about where your message lands. Everything below is about making that check pass consistently.
Your first setup, step by step#
- Ask your hosting or ESP provider to set a PTR for each sending IP.
- Use a hostname under your domain (mail1.example.com) rather than the provider's generic name.
- Create the matching A record so forward and reverse agree.
- Use the same hostname in the SMTP HELO/EHLO banner.
Words you will see#
- Mailbox provider: Gmail, Microsoft, Yahoo, Apple, and the corporate gateways that decide where mail lands.
- Authentication: proof that a message is from who it says it is (SPF, DKIM, DMARC).
- Reputation: the provider's running score of your domain and IP.
- Placement: whether a message reaches the inbox, spam, or is rejected.
Common mistakes#
- Generic PTRs like 203-0-113-10.provider.net.
- HELO names that do not match the PTR.
Frequently asked questions#
Can I set PTR records in my own DNS?
No. PTRs live in the IP owner's reverse zone. Your hosting provider or ESP sets them, though some offer self-service.