Is PEAR installed by default?

I know very little about PHP but need to move a PHP site temporarily to Webfaction before rewriting it to Django.

I tried to rewrite the below PHP file to use PEAR but I get no error message and don't receive any email.

<?php
require_once "Mail.php";
if(!empty($HTTP_POST_VARS['sender_mail']))
{
    $from_addr = "existing.address@webfaction-address.com";
    $to = "my@email.com";
    $subject =  "Test";
    $body = stripslashes($HTTP_POST_VARS['sender_name'])."\n".stripslashes($HTTP_POST_VARS['sender_email'])."\n".stripslashes($HTTP_POST_VARS['sender_phone'])."\n".stripslashes($HTTP_POST_VARS['sender_postal'])."\n".stripslashes($HTTP_POST_VARS['sender_code'])."\n".stripslashes($HTTP_POST_VARS['sender_city'])."\n".stripslashes($HTTP_POST_VARS['sender_country']);
    $body .= "\n\n---------------------------\n";
    $body .= "Mail sent by: " . $HTTP_POST_VARS['sender_name'] . " <" . $HTTP_POST_VARS['sender_mail']  . ">\n";

    $headers = array ("From" => $from_addr,
                      "To" => $to,
                      "Subject" => $subject
                      "Reply-To => "Reply-To: " . $HTTP_POST_VARS['sender_name'] . " <" . $HTTP_POST_VARS['sender_mail'] . ">");

    $smtp = Mail::factory("smtp", array ('host' => "smtp.webfaction.com",
                                         'auth' => true,
                                         'username' => "xxxxxxxxxxx",
                                         'password' => "xxxxxxxxxxx"));

    $mail = $smtp->send($to, $headers, $body);
    if ( PEAR::isError($mail) ) {
        echo $mail->getMessage();
    }
    else {
        echo "output=sent";
    }

} else {
    echo "output=error&info=no-email";
}
?>

Result is always output=sent but email is never received. I am using a Static/ CGI/ PHP app. Do I need to install the PEAR mail package? Does not seem like it as require_once "Mail.php"; does not give any error message.

Any easy way to debug?