how to validate correct email address

Question

Hi All,
I am new to ASP.Net and web development.
Question
I have a web form in that I have a button and a textbox control which accepts a email address. When I click on the button I want to validate the email address i.e., the email should be like this [email protected]
where somename can be any text or number or combination of both. And this somename can start with underscore/number/alphabets and can have dot in the middle and the email address should not start with otherthan underscore/number/alphabets and should not contain any special symbols(as in all providers such as yahoo,gmail,rediff,etc)
someprovider - like yahoo,google,etc
How to accomplish this
please help
Thanks
sachi