Redirecting users to my new pages with a message.

Hi,

As a customer request my application domain is changing. and i need to show
a popup message box saying that you are being redirected to the new site
since some users can bookmark the older url.

The application support team has configured both old and new urls to be
pointed to the same application instance.

Whats the best way to show users a splash screen when a users comes from the
old urls and redirect him to the new page.

Best Regards,