Any script tags posted on an ASP.NET web form will cause your site to throw and unhandled exception.
You can use a asp regex validator to confirm input, just ensure you wrap your code behind method with a if(IsValid) clause in case your javascript is bypassed.
If your client javascript is bypassed and script tags are posted to your asp.net form, asp.net will throw a unhandled exception.
You can use something like:
<asp:RegularExpressionValidator ID="regexEmailValid" runat="server" ValidationExpression="\w+([-+.]\w+)*@\w+([-.]\w+)*\.\w+([-.]\w+)*" ControlToValidate="tbEmail" ErrorMessage="Invalid Email Format"></asp:RegularExpressionValidator>