Reply To: How to Fix Error “No Valid MBOX file found” in MAC

Hey,
You can try this explain manual methods to fix your error related to ” no valid Mbox file” so that you can import your MBOX file to 10.7 platforms. To import Mbox from one platform, firstly you can take backup of your MBOX file using below instructions

First Go to library Mail Location: ~/Library/Preferences/com.apple.mail.plist

Sometimes files are hidden, to Open hidden files  Go >> Go to Folder.
Type ~/Library/ and click on Hit button, so that you can directly reach to mail location.
Now copy the  MessageRules.plist from the location and save them to the new location: ~/Library/Mail/V2/MailData/.
After taking backup of the file, now you can follow the instruction to import Mbox file in Apple mail.
Go to File >> Import Mailboxes >> Choose Apple Mail and click Continue button,
Now Browse the location of Mbox on your configured system. Select the Mbox file and select Choose button. Now click on Continue option.
Now close Mail.App application and reopen again to view the messages of imported file.

Hope this solution resolve your error of no valid Mbox files were found in Mac.