how can i add system.web.mail in to my windows application.

You could add a reference to the assembly which implements it and add its namespace to the IMPORTS section, but you don't have to use that assembly to use email. There is a message on this page just a few up from yours that describes this briefly. Simply add a reference to the DLL and IMPORT its namespace. Imports System.Web.Mail; To add the reference, go to the solution explorer and right-click on REFERENCES. Locate the DLL in the list on the .NET tab and select it. Click ok and it should show up in the REFERENCES list in solution explorer.