Why would you ever change format to back up?
Why would you export to back up?
Just copy and reuse the Outlook data file so you won't lose so much data.
The file you need to back up is your Personal Folders file (*.pst) It's
where all the mail, calendar, contacts etc are stored.
Take a look at these pages for info on Outlook data backup:
http://www.slipstick.com/config/backup.htm
http://www.howto-outlook.com/Howto/backupandrestore.htm

Signature
Russ Valentine
[MVP-Outlook]
>I export my out look data (contacts) to another folder as a back up when i
> import that file after formating my computer i got all of my contacts with
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>
> Zahid Aftab