To configure the SMTP service

1. Open the Exchange system manager and go to Global settings > Message Delivery > properties.
2. Select Recipient Filtering.
3. Select Filter recipients who are not in the Directory.
4. Go to Administrative Groups > First Administrative Group > Servers > [your server] > SMTP > the default SMTP virtual server > properties.
5. Select Advanced, then Edit.
6. Select Apply Recipient Filter, then OK.

Telnet to port 25 of your SMTP server and test the configuration.