This email from your techs is saying you can't use php mail() and you have to use PEAR mail... however I've tested your files and that doesn't seem to be the case.
It looks like you have an issue with your database connection on that page. I had to disable the check for unique username on line 27 and the insert into the database on line 43 before I could even get the email code to test fire.
Once I did that, and I enabled the "extra from parameter" option on the webassist/email/waue_registration_1.php page on line 15 I got the welcome email without issues.