How to use PHP Mail function or sendmail to send and/or receive emails from my live site
Based on the comments above:

Since your server does not permit direct SMTP communication, and since SMTP Authentication Support specifically overrides the default behaviour "This module allows Drupal to bypass the PHP mail() function and send email directly to an SMTP server."

I would suggest disabling the two modules, SMTP Authentication support and PHPMailer, and use the default drupal mailer which by default uses php mail() as permitted by the server.