Microsoft provides a step-by-step in Knowledge Base article Q302083:
This step-by-step guide describes how to configure the Internet Mail Service for Post Office Protocol version 3 (POP3) and Internet Message Access Protocol, Version 4rev1 (IMAP4) clients.
RequirementsYou need the following recommended hardware, software, network infrastructure, skills and knowledge, and service packs for this procedure:
- Exchange Server 5.5
- Operating system
Configuring POP3 and IMAP4 Internet Mail in Exchange Server 5.5To configure POP3 and IMAP4 Internet mail, you need to open the Internet Mail Service Routing properties, and then configure the Internet Mail Service.
Opening the Internet Mail Service Routing PropertiesTo open the Internet Mail Service Routing properties:
- In the Administrator program, click a site, and then click Connections.
- Double-click the Internet Mail Service that you want to configure.
- Click the Routing tab.
Configuring the Internet Mail ServiceIf the Internet Mail Service is not configured to reroute incoming Simple Mail Transfer Protocol (SMTP) mail, you may receive a non-delivery report (NDR) for any messages that you submit to recipients outside the organization by using POP3 or IMAP4 clients. To resolve this issue, configure the Internet Mail Service and resend the messages.
To configure the Internet Mail Service:
- Click the Routing tab, and then click Reroute incoming SMTP mail (required for POP3/IMAP4 support).
- Click Add.
- In the E-mail sent to this domain box, type the SMTP domain name of your organization.
- Click Should be accepted as "inbound".
- Click OK.
- Stop and then restart the Internet Mail Service.