Email Deliverability

Reverse DNS Missing

Reverse DNS (rDNS) maps an IP address back to a hostname via PTR records. Many mail servers require a valid PTR record that matches the sending server's hostname (Forward-Confirmed Reverse DNS or FCrDNS). Missing or mismatched rDNS is a strong spam signal and can cause emails to be rejected outright.

Symptoms

  • Emails rejected with "no reverse DNS entry" error messages
  • Gmail rejecting emails with "550-5.7.25" error
  • Anti-spam scores penalizing your sending IP
  • Mail server logs showing rDNS lookup failures

Common Causes

  • PTR record never configured at the hosting/ISP level
  • IP address changed without updating the PTR record
  • Hosting provider not offering PTR record management
  • PTR record hostname doesn't match the HELO/EHLO hostname

Step-by-Step Troubleshooting

  1. 1

    Check reverse DNS

    Look up the PTR record for your mail server IP address.

    Use Reverse DNS →
  2. 2

    Verify forward confirmation

    Ensure the PTR hostname resolves back to the same IP (FCrDNS).

    Use A Record Lookup →
  3. 3

    Check MX records

    Verify the MX record hostname matches the PTR record hostname.

    Use MX Record Lookup →
  4. 4

    Configure PTR at hosting provider

    Contact your hosting/ISP provider to set or update the PTR record for your IP address.

Recommended Diagnostic Tools

Reverse DNSA Record LookupMX Record Lookup

Monitor Reverse DNS

Track PTR record status and detect mismatches.

Related Problems

Frequently Asked Questions