on the success page, i added the following code to write the session contents:
<pre><?php session_start(); var_dump($_SESSION); ?></pre>
in the session, it contains the status of passing the email to the SMTP server, the status returned success:
string(98) "Sending To: email@example.com... Success
this means the email is being passed to the SMTP server, but the SMTP server is refusing to relay the email for some reason. you will need to contact the host for help in determining why the SMTP server is not relaying the email.