PHP email address correctness verification example

/**
* Verify email format
* edit: bbs.it-home.org
*/
$email="testgdy_007@163.com";
if (preg_match("/[a-zA-Z0-9]+@[a-zA-Z0-9]+.[a-z]{2,4}/",$email,$mail)){
    echo 'yes';
}else{
    echo 'no';
}
echo "$email??".$email."<>";
echo "$mail??".$mail;
?>