535 5.7.8: Authentication Credentials Invalid

🔢 Enhanced Status Code Breakdown: 5.7.8

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

💬 What This Error Means

The server didn't recognize your 'keys.' When your email software tried to log in to send your message, the server rejected the username or password. This is a setup problem on your end, not a problem with the person you're trying to email.

Common Causes

• A simple typo in your SMTP password
• You recently changed your password but haven't updated it in your mail app
• You need a special "App Password" (common with Gmail and Microsoft) that you haven't set up yet
• Your account has Two-Factor Authentication (2FA) enabled, which requires a different login method for apps
• Your username format is wrong (some servers need just "user", others need "[email protected]")

How to Fix This

• Double-check your username and password in your email settings
• If you use Gmail or Outlook with 2FA, generate and use an "App Password" instead of your regular one
• If you recently reset your password, make sure to update it in every app you use to send mail
• Contact your IT support or email provider to confirm your exact SMTP login settings

📚 Official Documentation

📋 Real-World Example Messages

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

535 5.7.8 Username and Password not accepted
535 5.7.8 Error: authentication failed: Invalid credentials

🔗 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.