Understanding External Access to Documents in an Office 365 Tenant (Part 1)

It’s a good idea to understand whether any external people have access to documents in your Office 365 tenant. There’s no option on the Office 365 or SharePoint Online consoles to tell you what access external users enjoy to SharePoint sites, so we must use some PowerShell to interrogate SharePoint and see what that reveals.
https://www.petri.com/external-access-documents-office-365-part-1