A messaging/collaboration architecture incorporating email with additional functions such as, scheduling, calendaring, instant messaging, and document management, and a client component for mailbox access. Individuals login and access their email account using a client (i.e. Outlook). Enterprise systems are more common to larger businesses. Three examples of enterprise messaging systems are GroupWise, Lotus Notes, and Microsoft Exchange. There are also small business versions of these commercial messaging systems as well as a large number of open source (free) alternatives. 

Storage Location

Email is delivered and remains stored on the mail server unless exported, archived or deleted.