Why does this happen

I have a mailer doohicky… and I just curious as to why something happens…

<?

// Mail out
$f = "From : ";
$From = $f . $email;
mail("5852611864@vtext.com", $subject, $message, $From);

?>

That code doesn’t send the e-mail address

<?

// Mail out
$f = "$From : ";
$From = $f . $email;
mail("5852611864@vtext.com", $subject, $message, $From);

?>

That one does… any clue why

also… is there a way to make it so when the user inputs their email address it actually shows up as coming from there?