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Bounce Decoder: 550 5.7.14

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550 5.7.14 — Trust Relationship Required

The 550 5.7.14 error means Microsoft 365 requires the sender to authenticate first via browser login. Learn what causes it and how to configure sending correctly.

🔴
Permanent Failure (Hard Bounce)
SMTP Code
550
Enhanced Code
5.7.14
Category
Trust Relationship Required
Frequency
Very Common

🔢 Enhanced Status Code Breakdown: 5.7.14

Component Value Meaning
Class 5 Permanent failure
Subject 7 Security or policy
Detail 14 Trust Relationship Required

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 requiring you to authenticate via a web login before sending email. This typically appears when a client is using Basic Authentication and the tenant has disabled it in favour of Modern Authentication (OAuth 2.0).

Common Causes

  • Microsoft 365 tenant has disabled Basic Authentication
  • Email client is not configured to use OAuth 2.0 / Modern Authentication
  • App or service using SMTP AUTH without the required permissions
  • Account requires multi-factor authentication that has not been completed

How to Fix This

  • Configure your email client or app to use OAuth 2.0 / Modern Authentication
  • For apps that cannot use OAuth, enable SMTP AUTH for the specific account in Microsoft 365 Admin
  • If MFA is required, complete the authentication challenge
  • Contact your Microsoft 365 administrator to check auth policies

🏢 Provider-Specific Variations

Microsoft 365 / Outlook

Microsoft 365 returns 5.7.14 when Basic Auth is disabled and the client hasn't migrated to Modern Auth. This is increasingly common as Microsoft rolls out Basic Auth deprecation.

📖 Microsoft 365 / Outlook 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

535 5.7.8
Authentication Credentials Invalid
534 5.7.9
Authentication Mechanism Too Weak

📚 Official Documentation

↗ Microsoft 365 SMTP Auth configuration ↗ Microsoft Basic Auth deprecation

🔧 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.

Run a Free Domain Authentication Check →
🔍

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