how to redirect external requests?

I want to configure Apache using .htaccess file so that any request from external web page should be redirected to splash.html but internal request should be not redirected for example :

if i'm on www.test.com and I clicked a link that leads to www.mysite.com it should redirect to http://ift.tt/1JTGqOs but if I request www.mysite.com from wwww.mysite/com/products it should take me to http://ift.tt/1dBYZ4T