Is there any way to "restore" a .pst (Outlook Personal Folder) or .ost (Offline Folder file)?

"I have had success with two different methods:

Method A

Save your pst/ost files (copy to a safe place via windows explorer)
Re-install Outlook and set up the account, but prevent it from downloading anything.
Note the location of the pst/ost files for the new Outlook installation
Close Outlook
Via explorer, replace the new installation's pst/ost files with your saved ones
Restart Outlook

Method B: Also I have used the previously mentioned Outlook import feature:

File > Import and Export > Import from another program or file > Personal Folder File (.pst) > locate PST/OST > Import

As for the difference between PST and OST files:

OST files cache the files from the exchange server; they are ""copies""
PST files exist only on one computer; they are not stored on the Exchange server"

"You can add PST files right into an existing Outlook configuration.

For Outlook 2007:

Tools / Options / Mail Setup tab / Data Files...
Then press the ""Add"" button, choose between the new format PST or the old 97-2002 format.
Then browse to where your file is located.

It should show then in the folder view of Outlook.

I also create local PST files for archiving ""stuff"". I then move the PST files when I get a new system, it's very handy. There are some Outlook systems that have policies that prevent creating PST files. Hopefully you won't get involved in that."

This project seems to work perfectly: github.com/mkorthof/ost2pst . No restrictions like all the other commercial tools that a Google search turns up.