Convert an offline Outlook .ost file into a portable .pst archive on Windows, locally, with no Outlook profile or Exchange connection. OST to PST Converter Software reads orphaned OST files too.
Drag the .ost into the window, or click Add File. You do not need the matching Outlook profile. Point the app straight at the orphaned cache, wherever you copied it from.
Set the output to PST. The folder tree from the source is kept as is, so Inbox and Sent and every subfolder land in the same place inside the new archive.
Click Start. The app reads through the whole OST, writes a valid Unicode PST, and leaves the original .ost untouched. Open the result in Outlook with File, Open, Outlook Data File.
The conversion is the easy part. What you keep is the reason to run it:
The reader opens a .ost with no Outlook running and no Exchange behind it, including a file whose MAPI profile was deleted. That is the case Outlook itself cannot handle, since it has no way to import an .ost.
The output is a Unicode PST with the same hierarchy as the source, Inbox, Sent, Archive, and nested subfolders, not a flat pile of loose messages. Empty system folders like Search Root are trimmed out.
Subject, HTML and plain-text body, sender, dates, the read or unread flag, and attachments all carry over unchanged, so the archive reads the way the mailbox did.
The window shows the OST as a tree with checkboxes. Convert the whole store, or tick a single folder. Handy when you only want one project's mail out of a 6 GB cache.
The result is a standard Outlook Data File that opens in Outlook 2016 and later. The source can be an OST cached from an Exchange or Microsoft 365 account, the OST to PST Converter Software does not care which server it came from.
A machine comes in with a leftover .ost and no working profile: maybe a departed employee, maybe a rebuilt PC whose Exchange cache got disconnected. You pull the mail into a PST for the record, and no need to stand the old account back up.
You left a job or the account was disabled, and the only copy of years of mail is the cached OST on your laptop. The server side is gone, but the file still has everything in it.
An old drive, a backup folder, a file Outlook now refuses to touch. Point the converter at it and save the parts that matter, with no account to recover first.
The two files look similar, but Outlook treats them very differently. That gap is the whole reason this tool exists.
OST to PST Converter Tool
9 Mb
1.0
07/07/26