SMTP authentication errors usually occur due to misconfigured email settings. Common causes include:

  • Incorrect username or password

  • Wrong SMTP server or port settings (typically port 587 for STARTTLS or 465 for SSL)

  • Email client not configured to use SMTP authentication

  • Firewall or antivirus software blocking outgoing SMTP connections

  • Account restrictions or temporary IP blocks from repeated failed login attempts

Make sure your email client is properly configured with the correct server details, and check any local security software that might interfere with sending email.

If the issue persists after checking all settings, contact our support team for further assistance.

For more help, see our tutorial: Troubleshooting common email issues in cPanel.

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