SharePoint Online external sharing
File sharing in Office 365 (Microsoft Office) for small business and enterprise users is available using the SharePoint Online environment. The SharePoint Online external sharing capabilities enables an organization to share documents with vendors, business partners or customers. Your company can view, share, and collaborate on your SharePoint Online sites as external viewers.
In SharePoint Online for enterprise the administrator allows sharing control for the whole company. Individual users within the company can then choose to activate the "external user invitation" feature. By default, sharing is turned off in SharePoint Online for small business. It can be turned on so the site owner can invite others to share documents via email.