Perpetual License for sale to Small and Medium Business customers.
Microsoft Exchange Enterprise User Client Access Licenses .
Built to deliver the enterprise-grade security and reliability that businesses require, Microsoft Exchange Server 2019 provides email, calendar and contacts on your PC, phone and web browser.
Microsoft Exchange Enterprise Client Access License (CAL) - designed to allow organizations to reduce the cost 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.
NOTE: 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.