Identify email address from link in an email

Question

Right now, we're identifying the recipient as a user by adding his/her email address to the URL of the link inside of the email. For example, a link in an email might be: http://something.com/?recipientEmail=cool_guy@aol.com

However, a problem was just presented - if the recipient of the email forwards the email, anyone that gets that message is also identified as the correct recipient when they click the correct link.

What other ways are there to identify the email address of the person who clicked the link? Or some other info that may solve the problem?

Answer 1

You can't, at least not exactly.

What you can do is use cookies to track the individual people who click your link, then assume that the first individual who clicks your link is the owner of the email that it was sent to, and that any other person is someone it was forwarded to.

What you can't do is determine who those other people are. You can only determine that they are probably different from the main recipient.