Email address already exists - Duplicate Email.

If you are under Daily, Customer and you are adding a new customer, or, adding an email address to an existing customer, and get the message that the email already exists. Check to see who has that email, by going to the customer search screen and put the email address in the email box. Press enter and the customer who already has that email will appear.

You should also check your inactive customers, if nothing appears when you first search by email, alone.