Import a Mailbox - OS X 10.7 - 10.8

To import a mailbox to another Mac’s Mail application follow the steps below.
1. Move the exported mailbox you would like to import to the destination computer. See Export a Mailbox - OS X 10.7 - 10.8.
2. Open the Mail application on the computer you wish to perform the import.
3. Select File from the top menu.
File

4. Select Import Mailboxes from the dropdown menu.
Import Mailboxes

5. A window will open titled Import. Choose Files in Mbox format at the bottom of the list.
Files in mbox format

6. Navigate to the location of the exported mailbox and select the .mbox file. Click the Choose button at the bottom of the window to complete the import.
Documents folder

7. You will now see a new mailbox entry under the Import section of the left hand pane titled mbox. You may click on the mbox folder to rename it to something more appropriate. For example the name could be something like 2012 Customer Email or johndoe@olympus.net mail archive.