🔢 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 SMTP server rejected your authentication attempt because the username, password, or credentials are incorrect. This is a sending configuration error, not a bounce from the recipient.

Common Causes

• Wrong password for the SMTP account
• Using an old password after a reset
• App-specific passwords required but not configured (Gmail, Microsoft)
• Two-factor authentication enabled but SMTP auth not updated
• SMTP username format incorrect (some require full email, others just the username)

How to Fix This

• Verify your SMTP credentials (username and password) in your email client or sending application
• If using Gmail, generate an App Password if 2FA is enabled
• If using Microsoft 365, check whether Modern Authentication is required
• Reset your email account password and update all configured applications
• Contact your email provider if the issue persists

🏢 Provider-Specific Variations

📋 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

📚 Official Documentation

🔧 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.