XFOR: Configuring POP3 Client for Remote Mail Configuration

The Internet Mail Service for Microsoft Exchange Server version 5.0 gives administrators the additional flexibility of using POP3 client software to connect to the Exchange Server computer. The Internet Mail Service does support POP3 as a server; however, there is currently no support for IMAP4 in Exchange Server 5.0.

Post Office Protocol, revision 3 (POP3)

The POP3 protocol uses the port 25 (SMTP) to send messages and port 110 (POP3) to download or retrieve messages from the server. In the default configuration in most POP3 clients available, POP3 downloads the messages to be stored locally and deletes them from the server. This was originally intended to reduce the amount of storage space needed on e-mail servers and to allow a light and fast e-mail client for the user.

Although this reduces the amount of storage space necessary on the server, it may not be convenient for some users who may use multiple clients to connect to servers such as Exchange Server.

For example, UserA uses the Exchange Server client in the office, but at home she uses the lighter, faster Internet Mail and News clients.

Internet Mail Access Protocol, revision 4 (IMAP4)

Like POP3, the IMAP4 protocol uses port 25 (SMTP) to send messages, but an IMAP4 server listens on port 143. Unlike POP3, IMAP4 allows the user to store messages by default on the server instead of downloading the messages locally.

For users of Exchange Server version 5.0 who want the convenience of IMAP4 with the storage located on the server, there is the following workaround.

To allow storage of messages on the Exchange Server, you can configure the POP3 client for a remote mail configuration. As part of the remote mail configuration, you also can configure the client to download copies of the message. This configuration allows you to read messages with the many Exchange clients and also to delete messages on the server when necessary.

Most POP3 e-mail clients have this configuration option, including Outlook Express included with Internet Explorer 4; Internet Mail and News; Windows CE Inbox; The Internet Mail Service for Windows Messaging included with Plus! for Windows 95, Windows NT Server, and Windows NT Workstation version 4.0; Netscape Mail; Eudora Pro; and others.

Additionally, the Internet Mail Service can be configured as a server for POP3 clients, but it cannot be a client to POP3 servers. The Internet Mail Service uses the SMTP port on port 25 to send and receive Internet mail. Although a POP3 account can send via SMTP on port 25, a POP3 account retreives mail on the POP3 port of port 110. The Internet Mail Service does not support this functionality, because this violates the original intent of the POP3 protocol.

For more information about configuring POP3 clients for a remote mail configuration, refer to the product documentation.

For additional information, please see the following articles in the Microsoft Knowledge Base: