How to Create Email Validation in ASP.net

Question

Hi,
I have different 5 aspx pages , In those 5 different aspx pages there are several asp.net controls.
Ex:
In Sample.aspx Page:
<asp:TextBox id="txt_canMailId" runat="server"/>

In Sample2.aspx Page:
<asp:TextBox id="txt_StMailId" runat="server"/> 

In Sample3.aspx Page:
<asp:TextBox id="txt_PosMailId" runat="server"/> 
I need to create one function in javascript and that function need to be use in all aspx pages.

I need to create one Javascript File  for all aspx pages to Check Email validation.


Please reply me.
Thanks, 
Suresh