PHP 抛出新的异常不起作用

我在PHP中创建了一个电子邮件类，但即使帖子数据为空，它也总是返回成功。异常显然不起作用，我想知道为什么它也没有发送任何电子邮件。代码如下：

<?php
class Contact
{
    private $toEmail = 'example@outlook.com', $subject = 'Personal Site - Contact';
    private $name, $email, $message;
public function __constructor(array $arr)
{
    if(!empty($arr['name']) && !empty($arr['email']) && !empty($arr['msg']))
    {
        $this->name = $this->ValidateName($arr['name']);
        $this->email = $this->ValidateEmail($arr['email']);
        $this->msg = $this->SanitizeMessage($arr['msg']);
        $this->SendMail($this->name, $this->email, $this->msg);
    }
    else
    {
        throw new Exception("Please fill all the required fields");
    }
}
private function ValidateName($name)
{
    if(ctype_alpha($name))
    {
        return $name;
    }
    else
    {
        return null;
    }
}
private function ValidateEmail($email)
{
    if(filter_var($email, FILTER_VALIDATE_EMAIL))
    {
        return $email;
    }
    else
    {
        return null;
    }
}
private function SanitizeMessage($msg)
{
    return htmlentities($msg);
}
private function SendMail($name, $email, $msg)
{
    $mailHeader = "From: " . $email . "'r'n"; 
    $mailHeader .= "Reply-To: " . $email . "'r'n"; 
    $mailHeader .= "Content-type: text/html; charset=iso-8859-1'r'n";
    $messageBody = "Name: " . $name . "";
    $messageBody .= "Email: " . $email . "";
    $messageBody .= "Comment: " . nl2br($msg) . "";
    if(mail($this->toEmail, $this->subject, $messageBody, $mailHeader))
    {
        return true;
    }
    else
    {
        throw new Exception('Message couldn''t be sent');
    }
}
}
try
{
    $obj = new Contact($_POST);
}
catch(Exception $ex)
{
    echo json_encode($ex);
}
echo json_encode('Message was sent succesfully');
?>