Hi Satish,
For your situation,
1) Have a separate YourErrorPage.aspx page designed in such a way that displays whatever common message you want to show.
2) In web.config file set
Then your application is configured for Custom Error Handling.
3) Now in the Page_Load of this page, add code to send email using "System.Web.Mail" classes.
Even you can get the information about the error source page in the querystring in this page.
It really works.
Try it..