email send request to user with database

Question

i have this code and i am trying to write code to send email or of the side or send to link of this side how can i write that code with database

<form action="mail.php" method="post">
<label for="email">your friend email</label>
<input name="email" type="edit"/>
<input type="submit" value="send link to friend"/>
</form>
<?
if (isset($_POST('email')) {
  if (!mail($_POST('email'), "Site link", "check this link " . 

$_SERVER['HTTP_REFERER'])) {
    echo "I couldn't send email, sorry.";
  }
}

?>

Answer 1

<?php
    if(isset($_POST['email']) && $_POST['email'] !== 0){
            mail($_POST['email'],'subject','message');
    } else {
        echo "Could not send email.";
    }
?>