Unable to Open an Old OST File After Outlook Profile or Mailbox Changes

If the original Microsoft 365 or Exchange mailbox still exists, create a new Outlook profile and let Outlook synchronize the mailbox again. An old OST file generally cannot simply be attached to another Outlook profile.

If the original mailbox is no longer available, keep a backup copy of the OST and first check whether the required data exists in a PST, backup, or retention location.

If the OST is the only remaining source, a third-party recovery tool may be required. EdbMails OST to PST Converter can scan an accessible orphaned or damaged OST, preview recoverable mailbox items, and export the readable data to PST. Recovery depends on the condition of the source OST.

After export, open the PST in Outlook and verify the folder structure, emails, attachments, dates, and important mailbox items.