You dont need to get an email to find your registration code if you bought the game from the SE store.
loggin in the store at https://store.na.square-enix.com
at the verry top of the page it lists
Square Enix --- Customer Support --- My Account --- Sign Out
click My Account
next click Your Orders
it dosnt say heavnsward, but it did have the price for it there, and click the view button under download page

Edit: at least this works for me now that I have regestered mine, dont know if it would have worked out before hand.