- substr: documentation ( source)
- str_repeat: documentation ( source)
- explode: documentation ( source)
<?php
$email = "h@hotmail.com";
$em = explode("@",$email);
$name = $em[0];
$len = strlen($name);
echo substr($name,0, $len/2) . str_repeat('*', $len/2) . "@" . $em[1];