Memeriksa apakah user melakukan POST

contoh form: 

<form name="new user" method="post" action="step2_check.php"> 
    <input type="text" name="mail"/> <br />
    <input type="password" name="password"/><br />
    <input type="submit"  value="continue"/>
</form>

cara ceknya :

if (!empty($_POST["mail"])) {
    echo "Yes, mail is set";    
}else{  
    echo "N0, mail is not set";
} 

cara cek salah :

if (isset($_POST["mail"])) {
    echo "Yes, mail is set";    
}else{  
    echo "N0, mail is not set";
}