OST to PST — an orphaned OST file that Outlook can open
Convert an .ost file to .pst in your browser: mail, folders, calendar, contacts and tasks, without the original account or Exchange.
About this conversion
An .ost belongs to one mailbox on one server, and Outlook refuses it the moment that mailbox is gone — after a job ends, an account is deleted or a profile is rebuilt. A .pst has no such tie: classic Outlook opens or imports it with no account behind it. This page reads the .ost and writes a new .pst record by record, so the folder tree comes across along with the mail, and so do the calendar, contacts and tasks rather than only the messages.
Just want to look inside it?
The same tool without converting anything: open a .ost file and read it.
You are not locked into PST
The file is parsed once and stays open, so the format is picked at the end rather than the beginning: the same .ost can leave here as CSV, XLSX, ZIP, EML, MBOX, PDF, HTML, TXT or JSON. Before that you can search it by subject or address, filter by year, sender and attachment type, mark the duplicates and look through the archive overview.
Questions
- Do I need the original account or Exchange?
- No. The .ost is read as a file; nothing connects to a server and nothing asks for a password.
- What comes across besides mail?
- Calendar events including recurring ones, contacts, tasks and meeting requests, each in a folder of the right kind, so Outlook shows the calendar as a calendar. Reminders that are long overdue are switched off, so Outlook does not greet you with years of alarms. Outlook's own sync logs (the Sync Issues folder) are left out.
- How do I get it into Outlook?
- Either open it as a separate data file (File → Open & Export → Open Outlook Data File) or merge it into your mailbox with File → Open & Export → Import/Export → Import from another program or file → Outlook Data File (.pst). The new Outlook for Windows opens .pst files only with a Microsoft 365 subscription.
- How large an .ost can it handle?
- The .ost is read in pieces and the new file is written in pieces, so the tab does not need memory for the whole mailbox; several gigabytes work. The finished .pst does need that much free disk space for the browser to save it.