This article was previously published under Q220865
If Microsoft Outlook Express or any SMTP/POP3 client is used as a messaging client in a Microsoft BackOffice Small Business Server (SBS) network, e-mail messages between users on the network function properly. Inbound e-mail messages from the Internet can also be received, assuming that there is a connection to the Internet through a dial-up Internet service provider (ISP) or a direct connection to the Internet. However, all outbound e-mail may result in non-delivery reports (NDRs).
The Internet Mail Service service, which is the component of Microsoft Exchange Server that makes sending messages over the Internet possible, is not configured to reroute SMTP-based mail automatically.
Also, Outlook Express does not send messages in Exchange format, so the messages that are sent bypass the Exchange Server information store, which would have told the Internet Mail service how to handle the message for successful delivery. The result is that the message is sent directly to the Internet Mail service. Because rerouting is turned off, the message does not get delivered.
To resolve this problem and turn on rerouting on the Internet Mail service:
Start the Microsoft Exchange Server Administrator program on the SBS-based computer. To do this, click Start, point to Programs, point to Microsoft Exchange, and then click Microsoft Exchange Administrator.
Start the Internet Mail service. To do this, double-click Connections, and then double-click Internet Mail Service.
Click the Routing tab.
Click Reroute Incoming SMTP mail (required for POP3/IMAP4 Support).
Click OK, and then restart the Exchange Internet Mail service.
After you follow these steps, Outlook Express users can send SMTP mail, but the SBS-based computer may be susceptible to unwanted junk e-mail messages. Servers with dial-up connections to ISPs are less vulnerable.