looks to me like you aren't setting the time on the cookie and as a result, it only lasts as long as the session. You need to set a time on it for it to last longer. For instance, in the script I built below, I first detected the current year, month and day and just tacked an extra year onto it.
$yr=(strftime("%Y"))+1;
$mn=(strftime("%m"));
$day=(strftime("%d"));
setcookie("cookie",$user['email'],mktime(0,0,0,$mn,$day,$yr),"/");
This makes the cookie last a year.