The handy part about the MBOX style backup is the restore is fairly painless. Its just a simple process of plugging in the username and MBOX backup into the sxmboximp command.
Lets say I have a user John Doe. John Doe's mailbox is completely corrupt and I am left with no choice but to delete the account and start over. I have the .mbox backup file that was created from the automated weekly backup I setup. The .mbox file is stored in [/backup/mailboxes] under the filename [John Doe.mbox].
To restore the users mailbox first and foremost I delete the corrupted mailbox. Then I recreate the users mailbox through the admin console. Once that is done I simply import all the messages from the .mbox file into the account
sxmboximp -u "John Doe" -a "/backup/mailboxes/John\ Doe.mbox" -s --listlevel folder
This will import the entire contents of the .mbox file to the users account. It will re-create folders if they do not exist and file messages just as they were when the .mbox file was created. The filename has a space in it so the extra \ is necessary when handing off the filename to the binary in unix. If the filename were [JohnDoe.mbox] with no spaces then the \ would not be necessary. I am assuming you are using the backup script I posted unmodified.