The task at hand is to validate the Textbox in asp.net for a valid email address.

We can attach a RegularExpressionValidator to the text box with the following regular expression:

<asp:RegularExpressionValidator ValidationExpression="^([a-zA-Z0-9_\-\.]+)@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.)|(([a-zA-Z0-9\-]+\.)+))([a-zA-Z]{2,4}|[0-9]{1,3})(\]?)$" ID="rxpEmail" runat="server"
ErrorMessage="Email Address is not valid" Text="*" Display="Static" ControlToValidate="txtEmail"></asp:RegularExpressionValidator>

Well i searched the net for the standards of a valid email id and i came across with a wonderful article at

I Knew How To Validate An Email Address Until I Read The RFC

It gives a an idea of what an exact RFC standard for the email id is.

I believe that we should follow validations which are quite obvious to the users and allow only standard email addresses.