Question: I want to schedule the email with asp.net and C# code.

what is basic idea or code for schedule email?

Answer: 
Try just writing a simple console app that sends the email and using Windows Task Scheduler to run it when you need it. Sending an email is a pretty standard task, like Will said, there are plenty of similar questions pertaining to it on here already, but if you have a look at the [System.Net.Mail](http://msdn.microsoft.com/en-us/library/system.net.mail.aspx) namespace, that should get you started.
The most simple way to differ the sending of email is to schedule a task in the windows scheduled tasks tool.
This task is a simple call to a vbs file.
This vbs file open an url from your web application.
Behind this url, put a webpage that do your scheduled work inside the app, in this case, the sending of emails.
It doesn't need windows service, just a simple vbs.
The called page is in your app, so no need to do some extra work to interface data or treatment outside of the web app.

Hope this will help,

Regards,

Pierre.