Microsoft positions Exchange Online as one way to reduce the workload of an IT staff. It takes time and effort to maintain an on-premises version of Exchange to ensure mail, calendars and other messaging features perform as expected.

Administrators must contend with regular patching via Patch Tuesday to maintain the stability and security of the Exchange deployment. The IT staff must also plot out an upgrade if their current Exchange Server version is due to move out of support, which might require purchasing newer equipment and developing a method to perform an upgrade without disrupting end users. With Exchange Online, Microsoft runs the service in its data centers and executes updates without downtime or involving an organization’s IT department.

A switch to Exchange Online can alleviate some of the hardware issues and problems with infrastructure components that can affect an on-premises Exchange deployment. Microsoft touts the stability of its service and offers a 99.9% uptime guarantee and a service-level agreement to provide a credit back to the organization if a disruption occurs.

Cost is another factor to consider when deciding whether to stay with Exchange Server or move to Exchange Online. Depending on the number of users and the frequency of server hardware upgrades, it might be cheaper to subscribe to Exchange Online for smaller organizations that buy new server equipment every three years.

Another benefit of Exchange Online is scalability. A cloud-based service can more quickly absorb a merger involving a significant number of users than if it had an on-premises Exchange deployment.

The other advantage of storing data in Microsoft’s data centers is not needing to develop and maintain the infrastructure for disaster recovery.

A drawback to Exchange Online is that disruptions will happen, and because Microsoft handles the support, it can be difficult to determine when the service will return.

Another drawback of Exchange Online is that Microsoft updates its cloud services on a frequent basis to add, remove and modify certain features. Users might get frustrated if some functionality changes or disappears when Microsoft pushes out an update. With an on-premises Exchange deployment, the feature set tends to remain fixed.

Some organizations might have to stop using certain third-party tools or applications that work with Exchange Server if they don’t integrate with Exchange Online. These organizations might want to maintain the level of flexibility provided by an on-premises messaging deployment.