What Is a Reverse DNS Lookup and Why Does It Matter for Email?

What Is Reverse DNS?

Standard DNS resolves domain names to IP addresses (forward DNS). Reverse DNS does the opposite — it resolves IP addresses back to domain names.

A PTR record (Pointer record) is the DNS record type used for reverse lookups. It lives in special zones under in-addr.arpa (for IPv4) or ip6.arpa (for IPv6).

For example, to find the PTR record for IP 203.0.113.5:

dig -x 203.0.113.5
# Queries 5.113.0.203.in-addr.arpa

Why Does Reverse DNS Matter for Email?

Receiving mail servers use reverse DNS as one of the checks when deciding whether to accept an incoming message. The check is called Forward-Confirmed Reverse DNS (FCrDNS):

1. The sending mail server connects and announces itself: EHLO mail.yourdomain.com
2. The receiving server looks up the PTR record for the connecting IP
3. The PTR record should return mail.yourdomain.com
4. The receiving server then looks up the A record for mail.yourdomain.com
5. The A record should return the original connecting IP

When forward and reverse DNS both match, FCrDNS passes. A mismatch, or a missing PTR record, increases the spam score of your outgoing mail and can cause outright rejection at some mail servers.

How to Check Reverse DNS

Using our tool

Enter any IP address in our Reverse DNS Lookup tool. You'll see the PTR record, the hostname, and whether FCrDNS passes.

Using command line

# Linux/macOS
dig -x 203.0.113.5

# Or using host
host 203.0.113.5

# Windows PowerShell
Resolve-DnsName -Name 203.0.113.5 -Type PTR

Common Reverse DNS Issues

Missing PTR record

Many IP addresses, especially on cheap VPS and cloud servers, have no PTR record configured. This is a significant email deliverability problem. Most hosting providers let you set a PTR record in their control panel.

Generic PTR record

ISPs often assign generic hostnames like 203-0-113-5.isp.example.com. This doesn't match a mail server hostname and fails FCrDNS. You need to request a custom PTR record from your hosting provider.

Mismatch between PTR and A record

The PTR record points to mail.yourdomain.com, but mail.yourdomain.com's A record points to a different IP. This causes FCrDNS to fail even with a PTR record present.

How to Fix Reverse DNS

1. Find your sending IP — the IP your mail server uses to connect to the internet
2. Log in to your hosting provider's control panel — look for "Reverse DNS", "rDNS", or "PTR Record" settings
3. Set the PTR record to match your mail server's HELO/EHLO hostname (e.g., mail.yourdomain.com)
4. Verify the A record — confirm mail.yourdomain.com resolves back to the same IP
5. Wait for propagation — PTR changes can take up to 24 hours to propagate
6. Verify with our Reverse DNS Lookup tool

Related Tools

• Reverse DNS Lookup — PTR record lookup for any IP
• PTR Record Lookup — Dedicated PTR checker
• DNS Health Checker — Full DNS health analysis for any domain
• DMARC Checker — Check email authentication records