title: Duplicate email address in MongoDB
body: <p>Gmail treats any email with dot (.) in it as the same as without dots. For example mail sent to hello@gmail.com or he.ll.o@gmail.com or he.llo@gmail.com will be sent to the same address. How will you store this in the database so that you avoid duplicate usage of emails with dots in it. For example if a user registers first with salman.khan@gmail.com , he should not be able to use any variation of the same email like sal.mankhan@gmail.com or salman.khan@gmail.com . (Assume the database have 10M of users).</p>