Exchange Server 2013 Enterprise User CAL
IMPORTANT NOTE: You must buy at least 5 CALS. New orders must also purchase a server license along with at least 5 Standard CALs.
The Enterprise CAL is sold as an Add-on to the Standard CAL. To enable Enterprise CAL features the user must be licensed with one Standard CAL plus one Enterprise CAL. The Enterprise CAL is designed to allow organizations to reduce the costs and complexity of meeting compliance requirements with new integrated archiving functionality and information protection capabilities while also helping you cut costs by replacing legacy voice mail systems with Unified Messaging.
A User CAL permits one user (using any device) to access or use Exchange server software. User CALs are likely to be more cost effective than Device CALs if there are multiple devices per user (for example a user has a laptop and handheld computer accessing Windows Server). A minimum of 5 CALs is required along with a server license.