I'm working on a simple registration email. I'm using MAMP (free) with PHP. I was getting emails from my code before. Now I get nothing. Here is a test code that doesn't send the email either.

<?php
$to = "[email protected]";
 $subject = "Hi!";
 $body = "Hi,\n\nHow are you?";
 if (mail($to, $subject, $body)) {
   echo("<p>Message successfully sent!</p>");
  } else {
   echo("<p>Message delivery failed...</p>");
  }
 ?>

What might have changed? I read that perhaps my ISP blocked sending emails? How do I find out?