No Access To Old Email Address

I have another Box account with an email that I do not have access to anymore and want to retrieve all my files that are stored on there.  How can I access my files on that account if I no longer have access to my old ISP's email address server?  I have read other post on this topic.  Am I out of luck if I can't gain access to my old email account?  And are all of my files on there not retrievable anymore?