Do you think it is possible to track sales using javascript in HTML email? I mean to put the tracking code in confirmation email when is the order is made instead of puting this at the "Thank you" page which is displayed after the client make the payment. Because confirmation email is sent after anti-fraud check this way I would get more accurate conversion stats.
Javascript is usually blocked by the email program and therefore is unlikely to be successful. The more usual way is to put in an unembedded image and the server counts the number of requests.
use a PHP file disguised as your logo or some other graphic - basically, mod_rewrite / htaccess redirect a file like logo.gif to track.php. within track.php do whatever tracking you need - you can embed it with parameters so you know who has looked at it etc... after you are done with the DB, just get contents of the real logo file and output to screen with the correct content type. its a pretty standard (and only way) to track EDM or any other email delivery. even so, there are no guarantees the recipient have allowed download of images automatically or even html emails.