Exchange Server 2013 Standard User CAL with Software Assurance through the Microsoft Open Business Licensing Program
IMPORTANT NOTE: You must buy at least 5 CALS. New orders must also purchase a server license
The Standard CAL is designed to help users be more productive from virtually any platform browser or mobile device. The Standard CAL works with either server edition.
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.