If isset POST

Question

I have a form on one page that submits to another page. What it does is it checks if the mail is filled but when I send an empty mail it just says it's set. 

step2.php:

<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>

step2_check.php:

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

What am I doing wrong here?