Exchange Online is Microsoft's cloud messaging platform, providing email, calendar, contacts and tasks. Users connect through Outlook, Outlook on the web or the Outlook mobile app and can use shared mailboxes, shared calendars and global address lists. Administrators work in the Microsoft 365 admin center and the Exchange admin center. It is delivered as software as a service, included in Microsoft 365 Business and enterprise subscriptions or bought as a standalone plan.
Microsoft is a US company headquartered in Redmond, Washington, and Exchange Online is proprietary. For a tenant provisioned in the European Union, Microsoft commits to store mailbox content (email bodies, calendar entries and attachment contents) at rest only within that geography. Enterprises can add Multi-Geo to place mailboxes in other geographies. As a US provider, Microsoft is subject to the US CLOUD Act, which lets US authorities compel production of data regardless of whether it is stored in the US or abroad. European organisations should weigh that alongside the residency commitment.