<form action="mail_gonder.php" method="post">
Alıcı : <input type="text" name="alici"/>
<br /><input type="submit" name="submit" value="Gönder"/>
</form>

<?
    $gonderen = 'test@test.com'; // Gönderen kişinin e-posta adresi
    $icerik = '<b> HTML MAIL </b>'; // E-posta içeriği (HTML)
    $konu = 'Test Mail'; // E-posta Konusu
    $alici = $_POST["email"];
    $hd= "MIME-Version: 1.0n";
    $hd .= "Content-type: text/html; charset=UTF-8n";
    $hd .= "X-Mailer: PHPn";
    $hd .= "X-Sender: PHPn";
    $hd .= "From: $gonderen<$gonderen>n";
    $hd .= "Reply-To: $gonderen<$gonderen>n";
    $hd .= "Return-Path: $gonderen<$gonderen>n";
    mail($alici,$konu,$icerik,$hd);
echo 'Gonderildi';
?>