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Fixing SMTP Authentication Errors in Easy WP SMTP: A Comprehensive Troubleshooting Guide

24 threads Sep 9, 2025

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Understanding and Resolving Common SMTP Authentication Failures

If you're using the 'Easy WP SMTP – WordPress SMTP and Email Logs' plugin and encountering authentication errors, you're not alone. Based on community reports, these issues frequently stem from configuration problems at the email service provider level rather than the plugin itself. This guide will help you diagnose and resolve the most common authentication errors.

Common Error Messages

The authentication errors typically appear in these forms:

  • "535 5.7.0 (#AUTH005) Too many bad auth attempts" - Your email provider has temporarily blocked authentication due to multiple failed attempts
  • "535 Authentication failed: The provided authorization grant is invalid, expired, or revoked" - Typically indicates incorrect credentials or an expired token
  • "535 5.7.139 Authentication unsuccessful" - Common with Microsoft 365/Outlook accounts, often related to security settings
  • "535 Incorrect authentication data" - Generic error suggesting credential issues
  • "535 5.7.139 Authentication unsuccessful, user password has expired" - The password needs updating despite working elsewhere

Step-by-Step Troubleshooting Solutions

1. Verify Your SMTP Credentials

Double-check your username and password. For services like Gmail, Office 365, or Zoho, ensure you're using the correct SMTP username format (usually the full email address). If you've recently changed your password, update it in the plugin settings.

2. Check for Account-Specific Requirements

Different email providers have specific requirements:

Microsoft 365/Outlook:

  • Ensure SMTP AUTH is enabled in your Microsoft 365 admin center
  • If Multi-Factor Authentication (MFA) is enabled, you must use an App Password instead of your regular password
  • Check if your password has expired (even if it works on other devices)

Gmail:

  • Enable "Less secure app access" or use App Passwords if 2FA is enabled
  • Check if you've exceeded sending limits

Zoho:

  • Ensure you're using the correct SMTP server for your region
  • Verify that third-party app access is enabled in your Zoho settings

3. Wait After Multiple Failed Attempts

If you see "too many bad auth attempts" errors, your email provider has likely temporarily blocked authentication attempts. Wait at least 30-60 minutes before trying again to allow the security lockout to expire.

4. Verify SMTP Server Settings

Ensure you're using the correct:

  • SMTP Host address (e.g., smtp.office365.com for Microsoft, smtp.gmail.com for Gmail)
  • Port number (commonly 587 for TLS, 465 for SSL)
  • Encryption type (TLS or SSL) that matches your port selection

5. Check for Sending Limitations

Some email providers impose daily sending limits. If you see errors mentioning "exceeded its 24-hour sending limit," you'll need to wait until the limit resets or upgrade your account if you regularly need to send more emails.

6. Review Email Content

If authentication succeeds but emails are rejected later in the process (e.g., "DATA END command failed"), your email content might be flagged as spam. Review your email content, subject lines, and avoid excessive links or spam-triggering phrases.

When to Contact Your Email Provider

If you've verified all settings and continue experiencing issues, contact your email service provider's support team. They can:

  • Check for account-specific restrictions
  • Verify SMTP access is properly enabled
  • Identify security flags on your account
  • Provide specific configuration details for your account

Remember that most authentication errors originate from the email service provider's security policies rather than the Easy WP SMTP plugin itself. The plugin successfully establishes connections but cannot bypass your email provider's security measures.

By methodically working through these troubleshooting steps, most users can resolve their SMTP authentication issues and restore email functionality to their WordPress site.

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