Who is your hosting company?
What have you entered for the SMTP server in the wa_globals.php file?
are the $WAGLOBAL_Verification_Email_FROM, $WAGLOBAL_Registration_Email_FROM and $WAGLOBAL_Password_Email_FROM all set to valid email addresses from your domain?
in the WA_Universal_Email/mail_PHP.php file, try changing:
$mailObj = mail($mailTo,$mailSubject,$mailContent,$mailHeader);
$mailObj = mail($mailTo,$mailSubject,$mailContent,$mailHeader, "-f".$mailFrom);
if all of the setting s are verified as correct, and it is still not working, then there is an issue with the smtp server refusing to relay the email for some reason, you will need to contact the host to have them look into the smtp server error logs to see why the relay is failing.