How do I get the email address of the person who clicked the link in the email?
Put a hash in the URL that uniquely identifies the address you sent it to.
I am working with Google App Engine python version. The app sends an 
email to the user with a link to a page to upload an image as an 
avatar. It would be nice to have the email so that I can associate the 
avatar with that email. How can I get the email of the person who just clicked the link? Thank you.