UpstairsPST & OST Viewer

You have a file nothing will open.

Upstairs reads Microsoft Outlook .pst and .ost mail archives, plus .mbox mailboxes from Google Takeout or Apple Mail, on your iPad and your Mac. The folders, the messages, the attachments, without sending any of it anywhere.

An export from a job you left. Your Gmail, downloaded from Google Takeout. A backup from a computer you no longer own. An archive someone handed you on a drive because it was the only way to hand it over. It is full of things you might need, and nothing on your Mac or iPad opens it.

Upstairs opens it.

What it does

Browse it like mail. Your folder tree, exactly as it was. Message lists with senders, dates and attachment markers. A reading pane that renders the message the way it was written.
Find anything. Full-text search across subjects, bodies, senders and recipients, matches highlighted in context. The whole archive, not just the open folder. Accents are ignored, so cafe finds café.
Get things back out. Export any message as a .eml that opens in Mail or Thunderbird. Save attachments. Export a whole folder at once.
Handle big archives. Ten gigabytes is not a problem. Upstairs memory-maps the file and indexes in the background, so you can read while it works.

Nothing leaves your device. Literally.

Most apps that say this mean they promise not to upload your data. Upstairs means something stronger and checkable: it ships without network permission at all. The app has no ability to open a connection, so the promise is not a policy that could change. It is a property of the binary.

You do not have to take our word for it. On a Mac, in Terminal:

codesign -d --entitlements - /Applications/Upstairs.app

com.apple.security.network.client is absent from the output. That is the entitlement an app needs to reach the network, and Upstairs does not have it.

No account. No sign-in. No server, so there is no database of you anywhere. No analytics, no crash reporting, no advertising identifiers. Remote images in messages stay blocked until you ask for them, so opening an old newsletter does not tell the sender you are still reading. And your archive is opened read-only, so Upstairs cannot modify it even by accident.

What's supported

Unicode .pst and .ost archives from Outlook 2003 onward, including compressed and encoded archives. And .mbox mailboxes, the format Google Takeout uses for Gmail exports and Apple Mail uses for its own, with Gmail's labels appearing as folders.

Two things are honestly not supported yet, and Upstairs says so clearly on screen rather than failing quietly:

The 32-bit ANSI format from Outlook 97-2002.
Outlook 2013 and later .ost files that use 4 KB pages.

Free and Premium

Browsing and search are unlimited and free, permanently. The free tier opens five messages, enough to confirm the archive really is what you think it is. Premium removes that limit and unlocks export.

Premium is a one-time purchase. There is no subscription. You buy it once, it covers your Mac, iPad and iPhone, and it stays yours on devices you buy later. Most people come here with one archive they need to get into, and charging a recurring fee for a job you do once would be wrong.