Log in to your Box account.
Click the drop-down menu on your name in the upper right-hand corner. Select Account Settings from the menu.
Verify the Account tab is selected.
Scroll down to the Login and Email Addresses section. Click Add More Emails.
Enter the new email address you want to use and click Save.
Box will send a confirmation message to your newly-added email address.
Click the Verify Email link in the email message you received to complete the setup.