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rDNS

rDNS

See why reverse DNS (rDNS) lookups matter for sender reputation and how to ensure your IP maps cleanly back to your domain.

rDNS / PTR (Reverse DNS)

Reverse DNS connects an IP address back to a domain name, helping inbox providers confirm who is sending the email.

What it is

rDNS, also called a PTR record, is a DNS record that maps your sending IP address back to a host name, such as `mail.example.com`.

Why it matters for deliverability

Inbox providers use rDNS to check if the server sending email looks legitimate. If there is no rDNS, or if it looks random, your emails are more likely to be flagged as spam.

How it works

For a given IP address, the receiving server performs a reverse lookup in special DNS zones (like `x.x.x.x.in-addr.arpa`) to get a host name. Often they also check that this host name has a matching forward DNS (A record) pointing back to the same IP.

Example rDNS setup

Example reverse DNS (PTR) configuration for IP address `203.0.113.25`:

PTR (reverse DNS): 203.0.113.25 → mail.example.com.

A record (forward DNS): mail.example.com → 203.0.113.25

Common problems
  • No PTR (rDNS) record set for the sending IP address.
  • PTR record points to a generic name like `server123.hostingprovider.com` instead of your domain.
  • PTR record and A record do not match (forward and reverse mismatch).
  • Using shared IPs where you cannot control the rDNS configuration.
  • Assuming rDNS can be edited in your domain DNS, when it is usually controlled by your hosting provider or ISP.
How to improve
  • Ask your hosting provider or email infrastructure provider to set the PTR record to a hostname on your domain (for example, `mail.yourdomain.com`).
  • Create a matching A record for that hostname pointing to the same IP.
  • Verify rDNS with online tools to ensure the reverse lookup shows your chosen hostname.
  • Avoid sending high-volume email from IPs that use generic or branded names of third-party hosts only.
  • If you use a cloud email provider, check their documentation; they usually handle rDNS for you.
Best practices
  • Ensure every dedicated sending IP has proper forward and reverse DNS alignment.
  • Use a hostname in rDNS that clearly relates to your brand (such as `mail.example.com`).
  • Do not change rDNS frequently; stability helps build reputation over time.
  • If you must change IPs, set up rDNS correctly before moving traffic to the new IP.
  • Combine correct rDNS with SPF, DKIM, and DMARC for a complete authentication setup.