Recover old outlook express mails

I'm trying to recover old emails from a hard drive. The contents of the "Outlook" folder I found on the drive look like the following:

21.04.17  13:54        23.885.168     Deleted Items.dbx
21.04.17  11:56            60.116        Drafts.dbx
21.04.17  13:54            74.720        Folders.dbx
24.10.16  13:41            74.720        Folders.old
21.04.17  13:54                 0            Inbox.dbx
24.10.16  15:42     2.147.431.408    Inbox.old
21.04.17  13:54             9.656         Offline.dbx
21.04.17  13:54         5.958.356      Outbox.dbx
21.04.17  13:54             9.404         Pop3uidl.dbx
21.04.17  13:48     1.246.232.048   Sent Items.dbx

I've managed to install windows live mail and import the mails from files with extension .dbx.

But I also need to import those with extension .old (The Inbox.old is about 2Gb large so there is definitely something there too).

I tried changing the extension of those files to .dbx too but nothing gets imported.

What should I do?