将信箱的某一段替换为

echo preg_replace('/(?<=.{3}).+@/', '*@', [email protected]');

$str ="[email protected]";
$sub = substr($str, 2,strpos($str,'@') -2);
$len = strlen($sub);
$replaceStr = str_repeat('*',$len);
$newStr = str_replace($sub, $replaceStr, $str);
var_dump($newStr);