Box for Outlook brings your secure Box content repository directly into your Outlook interface, enabling you to store email attachments and messages directly into the Box folder of your choice. Due to some recent changes made to enhance the security of Box for Outlook, users will need to re-grant the Box app certain permissions when they next use the integration. This is a one-time requirement and will not affect the user’s overall experience with the integration. They just need to follow the prompts to grant the necessary permissions and can then continue enjoying the seamless Box for Outlook experience.
You can read more about the changes Microsoft made here.