OneDrive for Business Access by External Users
Q: (from Bruce)
So, is it possible to Share with Everyone (including external people) in One Drive for Business?
If your organization has opted to enable sharing OneDrive externally, and you select to share a document or folder with “Everyone” it will only include external users that have been included explicitly by name in another share. There is no “anonymous” external sharing that allows anyone to access the document. As part of the sharing process, you can either invite the users with or without an email message.
Here are some official instructions including how to enable/disable external sharing for either SharePoint Online or OneDrive for Business: