550 5.7.25: Reverse DNS (PTR) Validation Failed
The 550 5.7.25 bounce means your sending IP has no valid PTR record or fails forward-confirmed reverse DNS. Learn how to fix this deliverability problem.
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550
5.7.25
Reverse DNS (PTR) Validation Failed
Common
🔢 Enhanced Status Code Breakdown: 5.7.25
| Component | Value | Meaning |
|---|---|---|
| Class | 5 | Permanent failure (Hard bounce) |
| Subject | 7 | Security or policy |
| Detail | 25 | Reverse DNS (PTR) Validation Failed |
Per RFC 3463 Enhanced Mail System Status Codes. Class (X) = severity, Subject (Y) = category, Detail (Z) = specific condition.
💬 What This Error Means
The receiving server couldn't verify your 'ID card.' It checked your sending IP address but couldn't find a valid 'Reverse DNS' (PTR) record that matches your domain. To many mail servers, this makes you look like a suspicious sender.
Common Causes
- Your sending IP address doesn't have a PTR record set up
- Your PTR record exists but doesn't match the domain you're sending from
- You're using a basic home or office internet connection that doesn't have professional mail settings
How to Fix This
- Contact your hosting provider or ISP and ask them to set up a "PTR record" for your IP address
- The PTR record should point to your mail server's name (like mail.yourdomain.com)
- Make sure that mail server name also points back to the same IP address in your regular DNS settings
📚 Official Documentation
Microsoft documents 5.7.25 for IPv6 only: "Access denied, the sending IPv6 address [...] must have a reverse DNS record". Anonymous inbound mail over IPv6 is opt-in for a Microsoft 365 organisation. Once it is on, a source IPv6 address without a valid PTR record gets the deferral 450 4.7.25.
📖 Microsoft 365 / Outlook documentation → Browse all Microsoft 365 / Outlook error codes →📋 Real-World Example Messages
These are real bounce message formats you might receive. Paste yours into the Bounce Decoder for instant analysis.
550 5.7.25 Reverse DNS validation failed for IP 550 5.7.25 [x.x.x.x] does not have a proper PTR record
🔗 Related Error Codes
🔧 Related Diagnostic Tools
These tools can help you diagnose and fix this type of bounce:
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