We can do a check to see if it is getting the the mail call that is sending the email. In Unviversal Email > mail_PHP.php do a search for the following line of code:
$mailObj = mail($mailTo,$mailSubject,$mailContent,$mailHeader);
It should be around line 254
Just after this line of code add in the following die statement so that the values used in the email will be printed to the screen:
$mailObj = mail($mailTo,$mailSubject,$mailContent,$mailHeader);
die("mail sent to the server with the following values: " . $mailTo . " " . $mailSubject . " " . $mailContent . " " . $mailHeader);
Give this a try and let us know what the result is, this will help us to determine if the mail is being sent to the mail server or if there is a failure that occurs before this.