Read carefully: accounts created before August 2016 are no longer usable and users from before that should register again.
Remember this:
If you don’t receive our mail in a few minutes, please check your email account’s Spam or Junk folder to ensure the message was not filtered.
If the message was filtered, you may find an option to “Mark as good” or “Add sender to white-list“. This will aid in receiving future emails from Box.