Until recently, users accessing their Microsoft Exchange Server mailbox from
a remote location used Dial-Up Networking (DUN) or Remote Access Service (RAS)
to dial their office and connect to the Exchange Server. This process usually
involved a long-distance phone call and contention for the dial-in lines at the
office. The release of Exchange Server 5.0 changes that scenario. Exchange 5.0
lets you access mailboxes on the server using Post Office Protocol 3 (POP3).
This development means that email clients, such as Eudora, Pegasus, or the
Microsoft Exchange client, that have the Internet Mail Service (IMS--formerly
Internet Mail Connector, IMC) installed can access regular mailboxes on an
Exchange email network over the Internet.
This article discusses installing and configuring support for POP3 on the
Exchange Server. To support access from clients on the Internet, you must also
install and configure the Exchange IMS to provide the requisite connectivity.
Exchange Server 5.0 includes both POP3 and the IMS software.
POP3 support is only a small part of Microsoft Exchange Server's
functionality. This article presupposes that you know how to set up and use
Exchange Server and the IMS. (For tips about installing Exchange, see David
Geiger, "Seven Tasks to Get Started with Microsoft Exchange,"
September 1996.) In addition, this article assumes that you are familiar with
the basic concepts of TCP/IP and of Simple Mail Transfer Protocol (SMTP)/POP3
messaging. For information about how to set up and use the IMC/IMS and a basic
tutorial about SMTP and POP3, refer to my book The Microsoft Exchange Server
Internet Mail Connector (Duke Press, 1997).
An example best explains the POP3 support. Figure 1 shows a
typical Exchange Server email system connected to the Internet. In this example,
an Exchange organization, SAKES, has one site, Athens. The server Kifissia has
several Exchange mailboxes and is running the IMS. The IMS is configured to
deliver mail using Domain Name System (DNS) for address resolution, and the LAN
is connected to the Internet via a permanent connection (for example, a T1 line
to an Internet Service Provider--ISP). Figure 1 also shows an SMTP/POP3 server
on the Internet at pop3.dcnw.com. SAKES is running Internet Shopper's NTMail on
this server and has four POP3 clients installed.
This configuration, which has been available since Exchange Server 4.0,
supports Exchange users trading mail with users on the Internet. The Exchange
users in the SAKES organization are running the Exchange client configured with
the Exchange Server delivery service; the IMS on Kifissia converts all mail
between the Internet and Exchange users. For example, when Exchange user George
sends mail to Internet user Judy, his mail is in an Exchange proprietary format
until it reaches the IMS on Kifissia. The IMS translates George's mail into
native SMTP format before forwarding it to Judy on the Internet. The process
occurs in reverse when Judy replies to George. (Chapter 2, "SMTP Mail
Basics," of my book describes this interchange in detail.)
All users in the SAKES organization use the Exchange client configured with
the Exchange Server service to send and retrieve their mail. This process
requires that users have an authenticated remote procedure call (RPC) connection
to Kifissia. This requirement is restrictive for Exchange users who need to
access their mail from a remote location. The RPC connection is also a problem
if you want to support third-party email clients, such as Eudora or Pegasus
mail.
Figure 2 shows a common scenario. The Exchange user Chris
connected to the Internet from a remote location, perhaps by dialing in to a
local ISP from a hotel room or connecting through a LAN at a customer's
location. Achieving an RPC-based connection to the Exchange Server under these
conditions is relatively difficult (but not impossible), and the standard
Exchange client configuration mentioned above is impractical. However, using the
POP3 support available in Exchange Server 5.0, Chris can access his mailbox to
send and receive mail without an RPC connection.