You can create a page in Episerver with that URL and then use the Shortcut feature (located under the Settings tab on every page) to select your external URL. You can read about Shortcut here http://webhelp.episerver.com/latest/cms-edit/all-properties-view.htm
You can also create a route in your code or just add an action method in your base controller, if you have one, and then handle the redirect there.
In my site I have a button target to www.mysite.com/registration but I don't have any content with that URL. I need to redirect this URL to an external URL like www.yoursite.com/registration.
Id there any out-of-box feature available?
Please provide the solution for this.