Supongo que es por esto
Código PHP:
Ver original$body= "Hello $uname, <br /><br />
This is your updated account details. <br /> User name: $youname <br /> Password: $newpassword<br /><br /> To log into your account with those details click the link below <br /> $server_url/login.php <br /><br />Please remember to change this password when you log in with something you can easily remember.<br /><br />------------------------------------------------<br /> This is an automated E-mail from <br /> $site_name ";
$headers = "From: " . $from . "\n";
estas enviando $newpassword por email y no envias $md5_newpassword, que croe que es lo que deberías hacer.