Using Microsoft Email Clients with Exchange Server

Configuring SMTP and POP3 in the Exchange client, Outlook, and Outlook Express

Last month, I gave an overview of how Microsoft Exchange Server supports the Simple Mail Transfer Protocol (SMTP) and Post Office Protocol (POP) 3 email protocols (for a list of related articles, see "Related Articles in Windows NT Magazine," page 169). In this article, I'll describe how Microsoft's Exchange, Outlook, and Outlook Express email clients use these protocols, as well as Internet Message Access Protocol (IMAP), with Exchange Server 5.5. To help you get a real-world understanding of how Exchange Server interacts with these protocols and email clients, I will provide examples from the small network that I described last month, which Figure 1, page 166, shows.

Exchange and Outlook MAPI Clients
Most companies using Exchange Server as their messaging server use the Exchange or Outlook email client on the desktop. Many users assume that the Exchange client that comes with the default Windows NT or Windows 95 installation will deliver mail to an Exchange server. However, the free Exchange client delivers mail to only a Microsoft Mail Post Office for a workgroup. To connect to an Exchange server, you must install the full Exchange client from the Exchange Server CD-ROM or the Outlook client from the Outlook CD-ROM. (For the appropriate client software, always obtain the latest version from Microsoft.)

When you configure the full Exchange or Outlook client, you must add a delivery service to Exchange. Screen 1 on page 169 shows the Microsoft Exchange Server delivery service in my Outlook profile. With this delivery service, my desktop client takes any message I compose and delivers it to the Exchange Server using the Messaging API (MAPI) protocol. For example, I use Outlook on Patmos to submit an Exchange message to Athena. MAPI is a proprietary protocol that Microsoft first implemented in Microsoft Mail. Microsoft supplemented MAPI significantly in Exchange Server. If I send mail to someone within my Exchange organization, the Message Transfer Agents (MTAs) on the Exchange servers in the organization transport my message as a Microsoft proprietary formatted binary object, and you can access the data for this object with the MAPI interface. The recipient will most likely read the message using the same type of MAPI delivery service profile I have for Athena (the recipient's delivery service points to the recipient's mailbox server). As I discussed last month, nothing in the configuration of the delivery service on Patmos lets you or prevents you from sending mail to recipients outside the organization. If you use MAPI to submit mail to an Exchange server, the universe of recipients is a function of the gateways you install on the network.

Exchange and Outlook POP3 Clients
Individuals who want to receive Internet email at home often sign up with a local Internet Service Provider (ISP). Typically, these users are buying a dial-up connection, an account on a POP3 server, and permissions to access an SMTP server. These users connect to the POP3 server to download their mail, and connect to the SMTP server to send their mail. The ISP might use UNIX or Exchange-based servers and applications to handle the mail, and individual subscribers don't know which type of SMTP mail system they are connecting to. For example, if you contract with Erols, a popular ISP in the Washington, D.C., area, you will connect to a UNIX host running Sendmail--a connection you can verify by looking at the response from Erols' host:

220 smtp1.erols.com ESMTP Sendmail 8.8.8/8.8.5

By contrast, when you connect to my friend Mark's SMTP server (as I discussed last month), you get an NT host running Exchange. The response from this host is:

220 arlington.minasi.com ESMTP Server (Microsoft Exchange Internet Mail Service 5.5.1960.3) ready

To send and receive mail, the subscribers can use any POP3 client. Your ISP might provide you with a popular freeware client such as the light version of Eudora or Pegasus, or you can configure your Microsoft email client to use the POP3 and SMTP delivery services. Again, many users have a misconception that the POP3 and SMTP delivery services are available with the free Exchange client that comes with the default NT and Win95 installation; however, you need to install the Outlook client from the Outlook CD-ROM or the Exchange client from the Win95 Plus! Pack or from the NT 4.0 CD-ROM to get these services. If you have the Outlook client, you get POP3 and SMTP protocol support when you add the Internet E-mail delivery service to your profile, as Screen 2 shows.

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In “Using Microsoft Email Clients with Exchange Server” (July), the description of Internet Message Access Protocol (IMAP) surprised me. My company’s experience and research has shown that one of the greatest benefits of the IMAP 4.1 protocol is the ability to remotely access and manage a message store on the server without needing to download a message except to read it. You can leave the original message on the server in the user-defined folder that contains the message. Please correct me if I am misunderstanding something about IMAP. 
--Eric Koester 

You are absolutely correct that IMAP 4 is a very rich protocol that supports storing read messages on the mail server. I caused some confusion in the July article by stating that “IMAP doesn’t let you keep copies of mail on the server, and it downloads your messages automatically to your mailbox when you double-click the message.” What I meant is that the Outlook Express client IMAP service automatically deletes mail from the server, compared with the Outlook Express Post Office Protocol (POP) 3 delivery service, which you can configure to leave a copy of messages on the server.
Exchange Server 5.5 certainly supports leaving read mail on the server. Any IMAP client that you can configure to do so will work correctly with Exchange Server 5.5. 
--Spyros Sakellariadis

Eric Koester August 11, 1999

In response to a September letter from a reader about how Internet Message Access Protocol (IMAP) works, Spyros Sakellariadis said, “What I meant is that the Outlook Express client IMAP service automatically deletes mail from the server, ...”
This statement is wrong. I’ve been using the Outlook Express IMAP client for about 18 months, and the only way to get it to delete messages from the server is to mark the message as deleted and purge the mail. The standard behavior is to keep all messages on the server and not get rid of even deleted messages unless specifically told to do so. 
--Nik Simpson 

In the section about deleted messages and the IMAP protocol in “Using Microsoft Email Clients with Exchange Server” (July), I was ambiguous about Exchange Server and wrong about Outlook Express (OE). After receiving a plethora of letters, I checked Exchange Server support and published the September letter in which I clarified the Exchange Server treatment and apologized for any misinformation. Unfortunately, I held my position on OE because I did not have the application with me, and I was sure my memory was correct. As Nik pointed out almost immediately, OE permits storing read and deleted messages on the Exchange Server system. When you read a message in OE, it flags the message in the Information Store (IS) as “seen.” When you delete a message in OE, it flags the message as “marked for deletion.” The message remains on the server, and a Messaging API (MAPI) client such as Outlook can still see and read the message. The only way to remove a message from the server using IMAP is to select Purge Deleted Messages from the Edit menu in OE and issue the Expunge command. This action permanently removes any message marked as deleted from the IS. 
Mea culpa. I apologize for my laziness, and thank y’all for keeping me honest! Now I know how Bill Clinton feels with each successive iteration of Ken Starr’s probe. 
--Spyros Sakellariadis

Nik Simpson August 11, 1999

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