What are your archiving settings? Do you have mails set to be moved to an
archive PST or just deleted?
Open your archive PST (File, Open, Outlook Data File) and see what's in the
various folders. Don't import/export, it breaks links and various other
things. If you don't know where your archive PST is select Tools, Options,
Other tab, AutoArchive button and look in the file path text box under the
"Move old items to:" radio button. If you can't see the entire path put your
cursor in the text box and click the End key.
If things are set to be deleted you're out of luck. If they're in the
archive PST you can access them from there or move things back but then
change your settings so things don't get moved again.