Is it possible to send a link to someone that a user can click to see information only they are privy to without using traditional query strings (ex ?x=y or ?a=b&c=d) in the URL yet STILL keep track of who has received and opened a message?
Sure. Just get their IP addresses, and use that to track them. You also might want to set cookies in the case of dynamic IPs, and have a one-time login required.
If you are using apache (might work on some other servers too) and it’s configured ok, you can also send a link like:
http://www.myserver.com/path/to/phpscri … CODE329nd/
which technically doesn’t include a querystring. In that case, apache will follow the folder structure down until it hits phpscript.php, at which point it will say “there’s more, but I know how to execute this thing, and it’s the end of the line on the filesystem” and run the PHP script.
Inside the script, you can use $_SERVER[‘REQUEST_URI’] to see what the client asked for, and parse the URL into its pieces and meanings from there.
You can also play around with mod_rewrite in apache to achieve similar and often cooler results.