Box describes this feature in greater detail on their support website here: Upload to Box Through Email - Box Support

To enable this on a folder you own, right-click it and choose Settings. In the Uploading section, there is a checkbox to select Allow uploads to this folder via email. Once this is checked, an Upload Email Address will be displayed. Be sure to click the blue Save Changes button at the top of the Settings screen.

Any files attached to emails sent to the Upload Email Address will be added to the Box folder, with some caveats:

• these email addresses are not managed by Technology Services, and so should not be used to transfer sensitive or protected information
• the subject and body of the email will be ignored; only file attachments are uploaded
• the email will be ignored if the total size of attachments is larger than 50MB
• the folder's owner will receive a notification when files are successfully uploaded
• collaborators and co-owners may also be alerted, if other notification settings are enabled