How to Convert an OST File to PST
Quick answer: To convert an OST file to PST, install the CoolUtils OST to PST Converter, point it to the .ost file, preview and select the folders you need, choose an output folder and PST format, then click Convert. It rebuilds a ready-to-open PST without Exchange or Outlook, works on corrupted files, and can batch many OSTs from the command line.
An OST is a local, cached copy of an Outlook mailbox. It is tied to the account and the profile that created it, so you cannot simply copy it to another PC and open it. To make the mail portable — to move it, archive it, or hand it to someone else — you convert the OST into a PST.
There are two ways to do it. If Outlook is installed, the profile still works and the account is still connected, you can export inside Outlook. When any of that is missing — the account was disabled, the profile is broken, or the file is orphaned or corrupted — you need a dedicated converter. Not sure which file is which? See OST vs PST explained.
Option 1: Export to PST inside Outlook
If your Outlook still opens the mailbox, use File → Open & Export → Import/Export → Export to a file → Outlook Data File (.pst), pick the folders and save. It works, but only under strict conditions:
- Outlook must be installed and the original profile must load.
- The Exchange, Microsoft 365 or IMAP account usually has to be reachable.
- It will not open an orphaned OST whose account no longer exists.
- A corrupted OST often fails to export, or drops items silently.
For a one-off, healthy mailbox this is fine. For everything else, skip it.
Option 2: Convert with a dedicated OST to PST converter
A converter reads the .ost directly and rebuilds a clean PST on your machine — no live account, no matching profile, not even Outlook required. The CoolUtils OST to PST Converter is the tool we use; it also recovers corrupted files and exports to PDF, EML, MSG and HTML in the same pass. Here is the exact process.
Convert OST to PST in five steps
Download the tool from CoolUtils and run it — the 30-day trial needs no credit card or email and installs without Outlook on the machine.
- Add your OST file. Point the converter at a single .ost or a whole folder of them. Orphaned files whose account is gone are fine; nothing is uploaded, everything stays on your PC.
- Preview the mailbox. Browse the recovered folders and messages, including items pulled from corrupted files, to confirm the data is there before you export.
- Select what to convert. Tick the folders you need and, if the mailbox is large, set a date filter so you only export the range that matters.
- Choose output folder and PST. Pick where the new file goes and select PST. You can also add PDF, EML, MSG or HTML for an archive copy, and set a split size for very large mailboxes.
- Click Convert. The tool writes a ready-to-open PST with emails, attachments, calendar, tasks and contacts preserved. Import it into Outlook with File and Open, or open it in any PST viewer.
How do I convert many OST files at once?
Use the command-line build. It converts a whole folder of OST files, including very large ones, unattended — drop it in a .bat file or a scheduled task and the batch runs itself.
OSTtoPST.exe "C:\Mailboxes\*.ost" -DstFolder "C:\PST" -Pst -Split 2000 -log log.txt
For a full side-by-side of the desktop tools, read our comparison of the best OST to PST converters. If you have no Outlook at all, see converting OST to PST without Outlook. You can also download the free trial and test your own file first.