importing mailboxes

Before I reinstalled OSX, I wanted to save all my emails I had saved on my computer and be able to reimport them in afterwards. There were a ton of emails, so I didn't want to do them all individually. So I simply dragged the folder from the left column out to my desktop, and it looked like everything was there no problem. Now I'm trying to reimport them in, but it keeps telling me there aren't any valid files to import. Any way I can get them imported? For example, one folder is named Work.mbox, and inside is a preference file and all the saved messages with .emlx extensions. I can open them individually and they will open up in Mail, but I can't get them to actually show up in Mail on the left column when I click the folder they're supposed to be in.

 

Awesome! I moved them in before, but didn't know about "Rebuild". Thank you Duff Man!