How can I restore my entire Sent Mail folder?

I want to restore my entire Sent Mail folder which I deleted in error. I was told to retrieve it from Time Machine, but when I open my mail application (Apple mail via Verizon) and then go to Time Machine and choose "Enter Time Machine' , I'm taken to FINDER. I can see Time Machine behind Finder, but I can't access it. FINDER is in the way. Can someone explain what I'm doing wrong?