A .pst file is a whole Outlook mailbox in one file - every folder, email, attachment, calendar entry and contact. It is what Outlook exports, what an employer hands over when an account is closed, and what sits in a backup from an old PC; an .ost is the copy Outlook keeps of a mailbox that lives on Exchange or Outlook.com. Without Outlook on Windows, neither opens - and Outlook for Mac cannot open an .ost at all. This reads both.
The mailbox is read in place, a slice at a time, rather than loaded into memory, so a file of several gigabytes opens as quickly as a small one. Browse the folders, read each message as it was sent - formatting and pictures included, with remote images held back until you allow them - save attachments, search subjects, senders and recipients across the whole mailbox (the first 500 matches are shown), and export a message as .eml, a folder as .mbox, the whole mailbox as a ZIP, contacts as vCard or CSV and calendars as iCalendar for Thunderbird, Apple Mail, Google, iCloud or an archive. It is free to use, with no account and no upload limit, and it runs entirely in your browser: nothing is uploaded, and while the page stays open, a feature you have already used keeps working offline.
- How do I open a PST file on a Mac?
- Open it here in Safari or Chrome - nothing to install. Outlook for Mac can import a PST but cannot simply open one to read, and cannot use an .ost at all. To move the mail into Apple Mail, save each folder as .mbox and use File, Import Mailboxes.
- Can I convert PST to MBOX or EML?
- Yes. The .mbox button saves every message in the open folder as one mailbox file that Thunderbird, Apple Mail and most mail tools import, and .eml saves the message you are reading as a standard email file, attachments included. ZIP saves the folder and the folders inside it with every email as its own .eml file, and Export all does the same for the whole mailbox, keeping Outlook's folder tree - with contacts as .vcf and .csv and calendars as .ics alongside.
- How do I get my contacts and calendar out of a PST?
- Open the Contacts folder and press .vcf for a vCard file that iPhones, Android, Google Contacts, iCloud and Outlook import, or .csv for Outlook's contact spreadsheet layout. Open the Calendar and press .ics, which Google Calendar, Apple Calendar and Outlook import. Repeating meetings stay repeating, in the time zone they were set up in, with occurrences that were deleted left out; a single occurrence that was moved or edited comes out at its usual series time.
- Can I save all the attachments at once?
- Yes. Attachments, above the message list, saves every attachment in the folder and the folders inside it as a ZIP (split into parts if it is very large). Files with the same name are numbered rather than overwritten.
- How big a PST file can it open?
- No set limit. The file is read in place, a slice at a time, instead of being loaded into memory, so a mailbox of many gigabytes opens without filling the computer’s memory. Exporting a very large folder as .mbox does build that file in memory, so a folder of many thousands of messages is best exported on a computer rather than a phone. The ZIP exports are written as they go: in Chrome and Edge straight into a folder you choose, so even the whole of a large mailbox does not have to fit in memory. A ZIP that would pass 3.5 GB or 60,000 files carries on in a second file, "(part 2)", and so on, as a single ZIP stops working past 4 GB; other browsers download it in parts of about 500 MB.
- What is the difference between a PST and an OST file?
- A PST is a standalone mailbox file - exported, archived or used by a POP account. An OST is the local copy Outlook keeps of a mailbox that lives on a server, such as Exchange, Microsoft 365 or Outlook.com. Both hold the same kind of content, and both open here.