Client Platforms for Microsoft Exchange

The very first order of business is to define what is meant by clients for Microsoft Exchange. The best way to do that is to compare and contrast an Exchange client with an Exchange correspondent (this term is the authors ‚ ). An Exchange client application has the ability to access an Exchange mailbox as the owner of that mailbox, whereas an Exchange correspondent has only the ability to send and receive mail to and from an Exchange user . If an Exchange mailbox were a physical mailbox at the post office, a client would have the key for accessing their mailbox, while a correspondent would only be able to send mail to that mailbox or receive mail sent from it.

An example of a client application is Microsoft Outlook 2003 . An example of a correspondent might be a user on the Internet. This latter functionality is enabled through Microsoft Exchange connectors or gateways. Applications that can only correspond with Exchange are also referred to as foreign mail clients . The users of foreign mail applications are defined as contacts within the Active Directory, as you learned in Chapter 5, ‚“Creating and Managing Exchange Recipients. ‚½ This allows Exchange users to address mail to the foreign mail users (Exchange interoperability with foreign systems is covered in Chapter 13, ‚“Connecting with Other Messaging Systems ‚½).

There are two main Exchange client application architectures:

MAPI (Messaging Application Programming Interface) MAPI is the Microsoft API used for messaging functions. Microsoft Outlook 2003 is a MAPI client, although it does not come bundled with Exchange Server 2003 as in previous versions of Exchange.

Following are examples of MAPI client applications that can still be used with Microsoft Exchange Server but are not necessarily supported:

• Microsoft Exchange Client (the version that shipped with previous versions of Exchange Server)

• Microsoft Schedule+ 7.5 (this product has been replaced by the Outlook Calendar function)

• Microsoft Outlook 97 version 8.03 (there are also versions of this product for Microsoft Windows 3. x , Windows 95, Windows NT, and Apple Macintosh)

Internet protocols Some Internet protocols can also be used by clients to access Microsoft Exchange. Examples are as follows :

Post Office Protocol version 3 (POP3) Retrieves mail from the Inbox folder of a mailbox on a remote server.

Internet Message Access Protocol version 4 (IMAP4) Retrieves mail from a mailbox on a remote server. Access includes personal and public folders, as well as the Inbox folder.

Hypertext Transfer Protocol (HTTP) Handles data transfer between World Wide Web servers and browsers.

Lightweight Directory Access Protocol (LDAP) Provides access to directory information. Clients and servers use LDAP to retrieve information from Active Directory. In previous versions of Exchange Server, clients used LDAP to access directories managed by Exchange.

Network News Transfer Protocol (NNTP) Transfers data between newsgroup servers and between newsgroup servers and newsgroup reader programs.

Figure 7.1 illustrates foreign mail users communicating with Exchange, and Figure 7.2 illustrates various types of Exchange clients communicating with Exchange.

Figure 7.1: Foreign mail user communication with Exchange

Figure 7.2: Exchange clients