From: DeskNow Knowledge Base
http://www.desknow.com/kb/

How do I restore mail from a backup?
http://www.desknow.com/kb/idx/9/122/article/

DeskNow by default does a nightly backup of all users' mail. This is configured in the Administration/Backup page.

User mail is backed up (within the configured backup folder) into the file usermail.tar.gz . tar.gz archives can be opened with most unarchiving programs, including WinZip in the Windows world, and obviously the tar command in Unix/Linux/Mac.

Imprtant: when restoring mail using the following instructions, if some emails were already present in the account/folder, they will not be replaced, but duplicated. To avoid duplication, either delete from DeksNow emails that are already in the backup, or delete from the backup emails already in DeskNow.

To restore all mail for an user account

from the usermail.tar.gz archive, extract the folder domainname/username to a folder on disk (ex. /temp/mail).

Then login into DeskNow as admin, click on Administration/Mail import and restore, and input the following parameters:

Source file folder on the server: /temp/mail

Destination account: user@domain.com

Destination mail folder in the account: (leave this field empty)

To restore a mail folder 'folder1' and its subfolders for an user account

from the usermail.tar.gz archive, extract the folder domainname/username/folder1 to a folder on disk (ex. /temp/mail).

Then login into DeskNow as admin, click on Administration/Mail import and restore, and input the following parameters:

Source file folder on the server: /temp/mail

Destination account: user@domain.com

Destination mail folder in the account: (leave this field empty)