I can see you're using an old version of Universal Email - these files are obsolete:
<?php require_once("webassist/email/mail_php.php"); ?>
<?php require_once("webassist/email/mailformatting_php.php"); ?>
Make sure you have the latest version of DataBridge installed, then double-click the Universal Email server behavior, check all the details and then click OK. This should update the page to use this file instead:
<?php require_once("webassist/email/WA_Email.php"); ?>
Make sure you remove the two lines mentioned above, and upload the new files & folders that should have been created in the webassist/email folder.