In this post we will configure the SMTP virtual server in Windows Server 2008 R2 to relay mail using Google.
Open IIS 6.0 Manager;
Right click the SMTP server and choose Properties;
Set your preferences for access and connection control and also relay restrictions.
Next choose the Delivery tab ~ Outbound Security;
Select Basic Authentication and enter your Google user name and password, then check “TLS encryption” and click OK.
Click on Outbound Connections;
Enter 587 as the TCP port, click OK.
Click on Advanced;
Enter smtp.google.com as the Smart host, click OK.
Click OK and you’re done.