I am working on a custom authentication module and part of the identifier that I am provided is the user's email address. The problem is that DNN allows multiple user accounts with the same email address, so it isn't as good a identifier as one would think.

Is there an easy way to prevent a user from creating more than one DNN account with the same email address? I know I can edit the code, but I am looking for a setting somewhere that I can use rather than modifying the portal code. My boss likes to install updates to the website without informing me, so it should be something that can exist beyond a site update.