Microsoft® Exchange Server 4.0 and 5.0 include Key Management Server (KMS), a combination certificate-issuing server and key-recovery server. KMS allows Microsoft Exchange users to send digitally-signed and encrypted mail to other Microsoft Exchange users. In a future release of Microsoft Exchange Server, all certificate-issuing functions of KMS will be replaced by Microsoft Certificate Server. This will allow Microsoft Exchange to take advantage of the flexible, standards-based capabilities of Microsoft Certificate Server. The KMS will continue to provide private-key recovery services. This will enable users and administrators to recover encrypted e-mail data in the event the user's private keys are lost or the user leaves the company.