The virtual SMTP server still exists in Server 2008 , much as it it did in Server 2003. You can follow these step to enable the feature.
Right-click on Computer and select Manage.
From the Service Manager Console and under Features select Add Features.
Select SMTP Server option. A pop-up window will appear, click Add Required Features button and then click next.
Click on Install and once complete, click Close.
Opening IIS 6.0 Manager under Administrative Tools -> Internet Information Services 6.0.
You may now configure the virtual SMTP server for your preferred domains.