Microsoft Exchange Online is a hosted messaging solution that delivers the capabilities of Microsoft Exchange Server as a cloud-based service. It gives users access to email, calendar, contacts, and tasks from PCs, the web, and mobile devices. It integrates fully with Active Directory, enabling administrators to use group policies, as well as other administration tools, to manage Exchange Online features across their environment.
Organizations that subscribe to Exchange Online retain control over the messaging services they offer to users, but they do not have the operational burden of on-premises server software. With the Exchange Online hosted plans described in this document, email is hosted on servers that support multiple customers simultaneously. These servers are housed in Microsoft data centers and are accessible to users on a wide range of devices from inside a corporate network or over the Internet.