Docs › Error Library › Authentication Errors › Error 535-5.5.4: Optional Argument Not Permitted for Auth Mode

Error 535-5.5.4: Optional Argument Not Permitted for Auth Mode

What Is Causing This Error?

This error arises when an email client or server uses an authentication command that’s either unsupported or incorrectly formatted for the server’s expected authentication mode.

This error specifically happens when an optional argument is provided with an AUTH command that does not allow for such arguments in its current configuration or operational mode.

Resolving the Error – Solution

To resolve the 535-5.5.4 error, you should:

  • Ensure that the authentication method and parameters used in your email client match exactly what is expected by the email server. This might involve removing any optional arguments that are not permitted for the chosen AUTH mode.
  • If you’re working with a WordPress site and encountering this issue in sending emails, configuring your SMTP settings with a plugin like Easy WP SMTP might help. It allows for precise configuration of SMTP authentication methods, potentially circumventing the issue by ensuring the correct AUTH commands are used.

That’s it! Now you know how to fix Error 535-5.5.4.

If you’d like to learn how to troubleshoot other common errors, check out the following tutorials: