MBox Office is a simple mbox viewer. It lets you restore your archived .mbox archives to any IMAP-supported email provider. You should be able to open mbox files using File -> Open.

Features

• Tested with iCloud, Gmail, Google Apps, Microsoft Exchange--it should work on most email accounts
• Supports multiple email accounts
• Native email browsing interface where you can restore specific emails
• Batch email restore--select all emails and click on "Restore Selected Emails"
• You import individual emails in .eml format to your existing .mbox file. You can use all the above mentioned features with it.