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?