Open an OST File, Then Convert It to PST.
Stuck with an .ost left behind by Outlook — maybe one with no account or server attached anymore? OST to PST Converter reads the file directly on your iPhone, iPad, or Mac, lets you browse every folder, message, and attachment inside, and converts the mailbox to a PST you can open on any PC — plus MBOX, EML, PDF, CSV, HTML, VCF, and ICS. Open it and browse for free; convert when you're ready.
100% offline · runs entirely on-device · no account · reads the .ost file directly · any mailbox size
An .ost is the offline copy of a mailbox that Outlook keeps on disk so you can read your mail when you're not connected. It normally syncs from a server, but the file itself holds a full mailbox — folders of messages with their attachments, contacts, and calendar events. The catch is that an .ost is tied to the profile that made it: copy it to another computer, lose the original account, or move to a Mac, and you're left with an "orphaned" OST that nothing will open. Outlook itself often refuses it with errors like "the file cannot be opened." OST to PST Converter from Rush Tools is built for exactly that situation. It works as both an OST viewer and a converter, reading the file directly on your iPhone, iPad, or Mac — with no original account, no server, and no upload.
Open an .ost and you can browse the whole mailbox: read messages with their attachments, page through every folder, and look over contacts and calendar events, so you can confirm it's the right file and find what you need. When you're ready to take that mail somewhere usable, the app converts it. The primary output is PST — a single data file you can open on any PC — so a mailbox trapped in an orphaned offline file becomes a portable archive again. From the same .ost you can also produce a single MBOX mailbox for Apple Mail, Thunderbird, or a Gmail import; a ZIP of standalone .eml messages; print-ready PDFs with headers and attachment lists; a CSV metadata table for spreadsheets; a browsable offline HTML copy; VCF cards for your contacts; and ICS files for your calendar.
Every conversion happens on your device. Your .ost is never uploaded to a server, copied to the cloud, or sent through any account — there's nothing to sign into and nothing phoning home, which matters when an offline mailbox holds years of personal or work correspondence. The app only reads from the source file and writes each conversion into separate output, so your original .ost is left exactly as it was. You can keep the full folder tree, preserve read and unread flags, skip duplicate messages, split large output into parts, or limit a conversion to a date range. After it finishes, it writes a transfer manifest that tallies the messages, folders, and attachments it moved, so you can verify nothing was dropped — and it handles gigabyte-sized mailboxes without choking.
A few honest points so you know exactly what this is. The app reads the .ost file on disk; it does not connect to or sign into Exchange or any mail account, and it doesn't need the original account or server — which is precisely why it works on orphaned OSTs. It opens and converts readable OST mailboxes, but it does not repair files that are corrupt or damaged. And for any "import into Outlook, your mail account, or Gmail" goal, the app produces a file you import yourself: the PST opens on a PC, and the MBOX imports into Apple Mail, Thunderbird, or Gmail. Opening an .ost and browsing what's inside is always free; converting and exporting are unlocked with a weekly or annual plan, or a one-time Lifetime purchase — no account on any of it.
One OST file, every format you need.
Outlook leaves an .ost copy of your mailbox on disk — and it still holds every message even after the account is gone. Open it to browse every folder, then convert what you need, starting with a PST you can open on any PC — all on your device.
OST → PST
A PST data file you can open on any PC — the primary conversion.
OST → MBOX
One mailbox file for Apple Mail, Thunderbird, or Gmail import.
OST → EML (ZIP)
Every message as a standalone .eml file, zipped.
OST → PDF
Print-ready pages with headers and attachment lists.
OST → CSV
A table of message metadata for any spreadsheet.
OST → HTML
A browsable, offline HTML copy of your mail.
OST → VCF
Contacts as .vcf cards for any address book.
OST → ICS
Calendar events for any calendar app.
From .ost to a file you can use.
Open the .ost file
Add the .ost left behind by Outlook — from the Files app, a download, AirDrop, or the share sheet — including an orphaned file with no account attached. It opens on your device; nothing is uploaded and the original is never changed.
Browse the mailbox
Read messages with their attachments and page through every folder, your contacts, and your calendar. Confirm it's the right mailbox and find what you need — all free.
Choose a format and options
Convert to PST for any PC, or to MBOX, EML, PDF, CSV, HTML, VCF, or ICS. Keep the folder tree and read/unread flags, skip duplicates, split large output, or filter by date range.
Verify and import yourself
Check the transfer manifest that tallies messages, folders, and attachments, then import the output yourself — the PST opens on a PC, and the MBOX imports into Apple Mail, Thunderbird, or Gmail.
Mail, contacts, calendar, attachments.
Browse every folder and message with its attachments, then convert.
Read the mailbox contacts and export them as VCF cards.
View calendar events and export them as ICS.
Open and save any attachment on its own.
A focused OST toolkit.
Convert OST to PST
Turn an offline OST mailbox into a single PST data file you can open on any PC — the practical way to rescue mail from a file Outlook itself won't open.
Browse Before You Convert
Read messages with attachments and page through every folder, contacts, and calendar inside an .ost — a full viewer and opener, not just an extractor.
Works on Orphaned OSTs
Reads the .ost file directly on disk, with no original account or server needed, so a file left behind by an old profile or a new computer still opens.
MBOX, EML, PDF, and More
Also convert to a single MBOX for Apple Mail, Thunderbird, or Gmail; a ZIP of .eml messages; print-ready PDFs with attachment lists; CSV; or an offline HTML copy.
Calendar and Contacts Export
Export contacts as VCF cards for any address book and calendar events as ICS files for any calendar app, straight from the same mailbox.
Conversion Options That Matter
Keep the full folder tree, preserve read and unread flags, skip duplicate messages, split large output into parts, or limit the export to a date range.
Transfer Manifest Verifies the Move
After each conversion the app writes a manifest tallying the messages, folders, and attachments it moved, so you can confirm nothing was dropped.
On-Device, Any Size
Opening, browsing, and every conversion run entirely on your iPhone, iPad, or Mac — no upload, no cloud, no account — and gigabyte-sized mailboxes are handled.
Opening, browsing, and every conversion run entirely on your device. Your .ost is never uploaded to a server, routed through the cloud, or tied to an account — no sign-in, no telemetry, no internet needed — and even gigabyte-sized mailboxes are handled on-device.
The app reads the .ost on disk with no account to log into and no server to reach. It never connects to or signs into Exchange or any mail account, which is exactly why orphaned OSTs left behind by an old profile still open here.
Opening an .ost and previewing the folders, messages, and attachments inside is always free, so you can confirm it's the right mailbox first. Converting and exporting unlock with a plan or a one-time purchase — no account.
- You switched PCs or lost access to Outlook, copied the old .ost across, and need to open it and convert the mailbox to a PST you can read on any computer.
- You found an orphaned OST left behind by a profile that no longer exists, with no account or server to reconnect, and need to get the mail out of it.
- Outlook keeps refusing the file with "the file cannot be opened," so you open it here directly and convert it instead.
- Moving an old mailbox into Apple Mail, Thunderbird, or a Gmail import by converting the .ost to a single MBOX file, then importing it yourself.
- An IT migration where you need a verifiable export — a PST plus a transfer manifest that confirms the message, folder, and attachment counts came across.
- Saving a few important emails as print-ready PDFs, building a CSV table of message metadata for a spreadsheet, or pulling contacts and calendar out as VCF and ICS.
Free to open any .ost file and browse the mailbox inside — every folder, message, and attachment, plus contacts and calendar, including previewing them. Converting and exporting — to PST, MBOX, EML as a ZIP, PDF, CSV, HTML, VCF, or ICS, with options like keeping the folder tree, preserving read/unread flags, skipping duplicates, splitting output, and date filtering — are unlocked with a weekly or annual plan, or a one-time Lifetime purchase. Your choice, and no account is required.
Opening & converting OST files.
What is an OST file?
An .ost is the offline copy of a mailbox that Outlook keeps on disk so you can read mail without a connection. It holds folders of messages with attachments, plus contacts and calendar. It's normally tied to a profile, so once that account is gone the file is hard to open anywhere — which is what this app is for.
Can I convert OST to PST without Outlook?
Yes. The app reads the .ost file directly on your iPhone, iPad, or Mac and converts it to a PST, with no Outlook involved and no account or server needed. You don't open the file in Outlook first — you open it here.
Is there a free way to convert OST to PST online?
Opening an .ost and browsing everything inside is free in this app, and converting is a paid feature. It is not an online uploader — your mailbox is read and converted entirely on your device, never sent to a server, which is the safer way to handle private mail.
How do I open an orphaned OST file with no account?
Just add the file. The app reads the .ost on disk and never tries to reach the original account or server, so an orphaned OST left behind by a deleted profile or an old computer opens and converts normally.
Outlook says the OST file cannot be opened — what now?
Open it here instead. The app reads the .ost directly rather than re-attaching it to a profile, so a file Outlook refuses with "the file cannot be opened" can still be browsed and converted — as long as the mailbox data itself is readable.
How do I open an OST file on another computer or a Mac?
Move the .ost to the device and open it in OST to PST Converter. It runs on iPhone, iPad, and Mac and reads the file directly, so it doesn't matter that the file came from a different machine or a profile that no longer exists.
Does it repair a corrupt or damaged OST file?
No. This app opens and converts readable OST mailboxes — it is a viewer and converter, not a repair tool. If the file itself is corrupt or damaged, it can't fix it. For a healthy or orphaned OST, it opens and converts the mailbox in full.
Will the PST it makes open on a regular PC?
Yes. The conversion produces a standard PST data file, which is the format a PC mail setup reads. You move the PST over and open it there yourself — the app makes the file; it doesn't connect to your account to import it for you.
How do I import the converted mail into Outlook or my mail account?
The app produces files rather than connecting to any account, so you import yourself. Convert to PST and open it on a PC, or convert to MBOX or EML and bring those into the mail setup you use. The app never signs into or touches your account.
How do I get OST mail into Apple Mail, Thunderbird, or Gmail?
Convert the mailbox to MBOX — one mailbox file that Apple Mail and Thunderbird import directly, and that Gmail accepts through its import. You do the import yourself, keeping full control of where the mail lands.
Which formats can it convert to?
OST to PST (a data file for any PC); OST to MBOX (one mailbox for Apple Mail, Thunderbird, or Gmail); OST to EML as a ZIP (one .eml per message); OST to PDF (print-ready pages with headers and attachment lists); OST to CSV (message metadata for spreadsheets); OST to HTML (an offline browsable copy); OST to VCF (contacts); and OST to ICS (calendar).
Can I keep my folder structure and read/unread status?
Yes. A conversion can keep the full folder tree intact and preserve read and unread flags. You can also skip duplicate messages, split large output into parts, and limit the export to a date range.
How do I know nothing was lost in the conversion?
After each conversion the app writes a transfer manifest that tallies the messages, folders, and attachments it moved. You can check it against what you expected to confirm the whole mailbox came across.
Does it connect to Exchange or sign into my account?
No. It reads the .ost file on disk and never connects to or signs into Exchange or any mail account. That's by design, and it's why a file with no live account behind it still works here.
Can it handle a very large OST file?
Yes. The app is built to open and convert gigabyte-sized mailboxes on-device, and the option to split large output into parts helps when the destination prefers smaller files.
Does converting change my original .ost file?
No. The app only reads from your .ost and writes each conversion into separate output. The original file is left exactly as it was, so you can convert it again to a different format any time.
What can I do for free, and what's paid?
Opening an .ost and browsing or previewing the folders, messages, attachments, contacts, and calendar inside are always free. Converting and exporting are unlocked with a weekly or annual plan, or a one-time Lifetime purchase — no account required.
Get the mail out of that OST.
Open the .ost — even an orphaned one — browse every folder, message, and attachment for free, then convert it to a PST for any PC, or to MBOX, EML, PDF, CSV, HTML, VCF, or ICS. All on your own device, with no account and no upload.