You do not need IIS in order to run Exchange Server, but IIS does enhance Exchange. For example, when using Exchange and IIS on the same server, all types of authentication supported by IIS may be used. However, with a separate server installation, only basic authentication may be used; Windows NT Challenge/Response authentication does not work.
Figure 3.3 Internet standards supported by Microsoft Exchange
Running in combination with IIS, Microsoft Exchange supports the following Internet standards:
Active Server components (HTTP protocol support) make it possible to access mailboxes, discussion groups, schedule information, and the directory on a Microsoft Exchange Server using any Web browser.
Use any POP3 mail client to read and send mail with Microsoft Exchange.
NNTP hosts Internet discussion groups, knowledge bases, and list servers on Microsoft Exchange, where they can be accessed using any Internet newsreader. NNTP also pulls existing Internet discussion groups into Microsoft Exchange where they can be replicated and viewed throughout the enterprise.
Exchange clients can take advantage of secure communications using SSL.
Allows access to the Microsoft Exchange directory using LDAP client.
Microsoft Exchange ensures secure communication between an Internet mail reader (POP3), Internet newsreader (NNTP), or LDAP client and a Microsoft Exchange Server.