550 5.7.14: Trust Relationship Required

🔢 Enhanced Status Code Breakdown: 5.7.14

Per RFC 3463 Enhanced Mail System Status Codes. Class (X) = severity, Subject (Y) = category, Detail (Z) = specific condition.

💬 What This Error Means

Microsoft 365 is asking for a more secure login. It doesn't quite 'trust' the way your email app is trying to connect. This usually happens because you're using an older login method (Basic Auth) that Microsoft is phasing out in favor of 'Modern Authentication' (OAuth 2.0).

Common Causes

• Your company has disabled older, less secure login methods
• Your email app is outdated and doesn't support the latest security standards
• You have Two-Factor Authentication (MFA) enabled but haven't completed the challenge in your app

How to Fix This

• Update your email app to the latest version to ensure it supports "Modern Authentication"
• If you're using a custom script or app, you may need to switch to using OAuth 2.0
• Check with your IT admin to see if they need to specifically enable "SMTP AUTH" for your account
• Look for a sign-in prompt or notification on your phone to complete your security check

📚 Official Documentation

📋 Real-World Example Messages

These are real bounce message formats you might receive. Paste yours into the Bounce Decoder for instant analysis.

550 5.7.14 Access denied. The user needs to sign in first.
550 5.7.14 <https://aka.ms/mfasetup>

🔗 Related Error Codes

🔧 Related Diagnostic Tools

These tools can help you diagnose and fix this type of bounce:

🔧 This Bounce Is Related to Email Authentication

Fixing this type of bounce requires correctly configured SPF, DKIM, and DMARC records. Our free Domain Checker analyses all three in one scan and tells you exactly what to fix.