Gabak,

Since your not using an exchange account, no OST file is created. Only a .PST or Offline folder for back up reasons. IMAP will only have your Email and Email folders within the PST file. Making a back-up is to simply export a copy of your mailbox to a separate .PST file. Any .PST file can be opened within Outlook without having to import it back into your mailbox.

If you want a back up of your contacts, simply export copy to a CSV file.

Hope this helps