How can I connect Microsoft Exchange Server to another mail system that hosts mailboxes for a certain SMTP namespace?

Start Exchange System Manager (ESM--Start, Programs, Microsoft Exchange, System Manager).

Expand the Administrative Groups, then expand Routing groups until you see the "Connectors" branch.

Right click Connectors and select New, SMTP Connector.

Enter a descriptive name for the connector in the Name field (e.g., Exchange London to widget.test Notes), as the figureshows. Select "Forward all mail through this connector to the following smart hosts" and in the text box, enter the DNS name of the other mail system or its IP address. If you enter the IP address, place it in square brackets (e.g., [192.168.1.50]). Under "Local bridgeheads," click Add.

Select the "Address Space" tab and click Add. In the displayed dialog box, select the address type (in this case, SMTP) and click OK. Enter the E-mail domain (e.g. *.widget.test) as the figure shows, and enter a cost between 1 and 100 (the lower the cost the higher the link's precedence).

If you want this connector to be available to the entire organization, select "Entire organization" under Connector's scope, as the figureshows. Then select the "Allow messages to be relayed to these domains" check box.

Navigate through the other tabs for options that might apply to your environment, then click OK.