Hi there, 

Welcome to Box Community and glad to assist! 

If you can’t access the email address associated with your Box account, we recommend either contacting your email service provider (ESP) to regain access to your email account or creating a new account.

Box is unable to help you regain access to your email account. You must have access to the email address associated with your account to change your account password. This security procedure enables us to protect your account against unauthorized access. 

For your reference, please see this article. 

Thanks for posting!