To export (archive, back-up) mail folders:

1. Open Outlook.
2. Click File→ Open & Export → Import and Export.
3. Choose Export to a file, then select Outlook Data File (.pst).
4. Pick the folder to export (if you choose the topmost folder where it says Mailbox and check the include subfolders box all of your Outlook data will be exported).
5. Decide where to save the exported file to using the Browse button.
6. Decide what to do with duplicate data in case it happens. Use the default if you are unsure.
7. For most people no encryption is fine, but if you really need it then be sure to remember your password.

To import folders back in:

1. Open Outlook.
2. Click on the folder where you want to import your data into first.
3. Click File→ Open & Export → Import and Export.
4. Choose to Import from another program or file.
5. Select Outlook Data File (.pst) and then Browse to find the file to import.
6. Choose your options regarding duplicate items.
7. Select the folder to import from the list of folders that you backed up. Check the include subfolders box if you want folders within the top level folder to be imported.
8. Choose to import into the current folder you selected when you started or into the same folder. Please take note of the same folder option, as you can easily clutter one of your real folders this way by accident.