Microsoft Exchange and IMAP are both email servers where messages are stored and retained on the email server. Unlike POP3, inbound and sometimes outbound messages are saved on a central server which can be accessed via webmail or with an email client such as Microsoft Outlook.

The primary difference between Exchange and IMAP is that Microsoft Exchange is a much more robust platform. IMAP tends to be used in organizations who are looking for simple mail server hosting.

Exchange servers offer much more features over IMAP, such as shared calendaring, address books and scheduling options. Exchange is generally better for small to mid sized corporations with 40-1000 users.

IMAP is a good solution for small offices which need to retain emails on a centralized server. It is generally open source, which means there are no licensing fees. Companies need only pay for server maintenance and administration costs.