Scenarios for Coexistence of the POP3 Service in Exchange Server 2003 and Windows Server 2003

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This topic explains how to configure coexistence between the Microsoft® Windows Server™ 2003 POP3 service and Exchange Server 2003. It explains two basic scenarios in which the Windows Server POP3 service and Exchange Server can coexist within an organization:

  • Windows Server POP3 and Exchange Server users coexisting and sharing the same SMTP mail domain; that is, the SMTP address for which mail is accepted for users.

  • Windows Server POP3 and Exchange Server users coexisting and using different SMTP mail domains.

In either scenario, Windows Server POP3 users and Exchange Server users can coexist in a single Active Directory forest. The basic configuration relies on the following principles:

  • Exchange users are created as mailbox-enabled users and granted access to a mail client such as Microsoft Outlook® or Outlook Web Access   Basically, your Exchange Server users exist as they would in most standard deployments.

  • All users (both Exchange Server users and POP3 users) use a single authentication method through Active Directory   POP3 supports additional authentication methods, which are not discussed in these scenarios.

  • The mail domain on the POP service is different from the mail domain in Exchange   Exchange and a server running the Windows Server POP3 service cannot use the exact same mail domain because mail-looping occurs when e-mail is sent from a user in one system to a invalid user on another system.

  • Each POP3 user exists as a mail-enabled user account in Active Directory   You must use the Exchange Tasks Wizard to mail-enable each user account and assign the account an external e-mail address matching the SMTP mail domain that you want to share. If you do not configure this account, Exchange does not recognize these users as possible recipients for mail it receives. This configuration also allows POP3 users and Exchange Server users to view each other in the global address list.

  • The Windows Server POP3 service clients are configured to use authentication on their outgoing mail server   To send e-mail to external users, POP3 users must authenticate on the SMTP server on Exchange Server.

  • An SMTP connector is created to route mail to the server running the Windows Server POP3 service   The connector allows messages to be routed to POP3 users in this domain.

  • The SMTP service on the server running the Windows Server POP3 has permission to relay through Exchange Server   Exchange Server must be configured as a smart host and the Windows POP3 service must have permissions to relay.