I have windows 11, Microsoft 365 Classic Outlook. I want to change from the .ost inbox file to the ,pst data file.

An .ost file cannot simply be changed into a .pst file. They serve different purposes in Outlook.

• .ost is the offline cache used by Exchange, IMAP, and similar accounts.
• .pst is an Outlook Data File used for local storage, export, backup, or POP data.

For Classic Outlook on Windows 11 with Microsoft 365, the supported options are:

1. Change the location of the .ost file by creating a new Outlook profile and selecting a different .ost path during setup.
   • In Control Panel > Mail > Show Profiles > Add
   • Create the new profile
   • After Outlook finds the account, select Change account settings
   • Go to More Settings > Advanced > Outlook Data File Settings
   • Select Browse and choose an existing .ost file or specify a new location for a new .ost file
   • Finish setup, then in Mail, select Always use this profile and choose the new profile
2. Use the ForceOSTPath registry value to set a different .ost location for a new Outlook profile. Warning: Editing the registry can cause serious problems if done incorrectly.
   • Open Run, type regedit, and select OK
   • Go to HKEY_CURRENT_USER\Software\Microsoft\Office\xx.0\Outlook
   • Create a new Expandable String Value named ForceOSTPath
   • Set its value to the full folder path where the .ost file should be stored, such as D:\MyOST
   • This works only for a new Outlook profile
3. If the goal is to store or back up mail in a .pst file, export mailbox data from Classic Outlook:
   • File > Open & Export > Import/Export
   • Export to a file > Outlook Data File (.pst)
   • Select the account, keep Include subfolders selected, choose where to save the .pst, then finish
4. If a .pst file already exists and the goal is to open it in Outlook, use:
   • File > Open & Export > Open Outlook Data File

A .pst file can be opened alongside the mailbox, but it does not replace the .ost inbox file for an Exchange or IMAP account.

• You can't change the location of the offline Outlook Data File (.ost) in Microsoft Outlook
• Export emails, contacts, and calendar items to Outlook using a .pst file
• Why does an Outlook profile not work with a .ost datafile? - Microsoft Q&A