Steps to Do:
DataBase:
1.Add token column(any name),received column to your database table which has id,pwd,....
AspCode(In .Cs file)
1.Generate token by using "random" keyword and send token,id(which is already have) as a query string in url to mail account like
htttp://www.Testmail.com/home.aspx?token=1234&&id=123;
2.When user clicks on link(which is present in gmail or any other mail.).he is redirected to home page.
3.In home page you need to get the values from token and id and write the logic to update the column "received" to yes.(or you can use any logic).
NOTE:
1.If you want secure for token you can use encrypt and decrypt logic for token
2.The answer to this question is not a logic.its a task.So for time sake i just give the logic.For more you need to study various articles then you will get a clear idea.
refer below links .you will get an idea.
mail confirmation in asp.net[
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http://forums.asp.net/t/1742559.aspx?Email+confirmation+link[
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http://stackoverflow.com/questions/20738351/sending-email-confirmation-link-in-an-asp-net-application[
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http://aspsnippets.com/Articles/Send-user-Confirmation-email-after-Registration-with-Activation-Link-in-ASPNet.aspx[
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