I have found MailDir folder, and all files in it. Now i have copied them on usb stick.
Are you seeing these on the old drive or in the USB backup? If you are seeing the three folders I mentioned in the previous post in the .tgz file on the usb stick, and the last file in etc/ is smbpasswd, You should have a valid backup and we can work with the restore process.
Are you still able to boot the old server? If the answer is yes, I would suggest another try at backing up the server.
How much data is on the server? If you have less then 2gb you should be able to use the server manager backup and restore option.
How many users do you have on this machine?
It is possible to manually copy the files into the maildirs on the new machine, however it is not a job for somebody who is unfamiliar with linux as you will more then likely have to change all the user:group ownerships and rights on the files.