Exchange Server 2019 Client Access Licenses (CALs) are required to enable access by users and devices to the extensive communication and collaboration features of Microsoft Exchange Server 2019. CALs secure the rights to use email, calendar, and contact functions as well as other communication features that Exchange Server provides for businesses. There are two main types of CALs that are tailored to different usage scenarios:

User CAL: This license allows a specific user to access the Exchange Server from multiple devices. It is ideal for mobile employees or users who work on multiple devices and therefore require greater flexibility.

Device CAL: This license is assigned to a specific device that multiple users can access. It is particularly suitable for workplaces with shared devices, such as in shift work or at public workstations.