Table of Contents
What is an OST file?
OST is the abbreviation for Offline Storage Table; whenever you add an Exchange, Microsoft 365, or IMAP account to Outlook, the system will create one automatically and you won’t see this taking place.
The copy of your mailbox is stored on your disk. You can read your mail on a plane, correct a draft in a taxi, or check tomorrow’s meetings even when there’s no signal at all. When you’re back online, Outlook sends your changes to the server. The file will only function with the profile that created it; if you copy it to a new laptop, Outlook will ignore it.
What is a PST file?
PST stands for Personal Storage Table and all items such as emails, contacts, calendars, and tasks are stored within a single file. Emails from POP3 accounts are saved into a PST by default, and it is also possible for you to export any mailbox into a PST yourself.
There’s no need for a server—just put it on a USB stick, insert the stick into another computer, and open it by selecting File > Open & Export. That’s all.
OST vs PST: Key Differences
| Feature | OST | PST |
|---|---|---|
| Main job | Offline copy of a mailbox | Backup and archive |
| Syncs with server | Yes | No |
| Portable | No | Yes |
| Created by | Exchange, M365, IMAP accounts | POP3 accounts or manual export |
| Password protection | No | Yes |
| Default size limit | 50 GB | 50 GB |
The greatest difference lies in syncing. Since an OST remains connected to the server, if a message is deleted in Outlook it will also be removed from the mailbox. A PST, on the other hand, is independent and so if you delete an item from it the server will not be made aware of it.
Further gaps can be seen as a result of this. It is not possible to transfer an OST to another profile, but it is possible to transfer a PST to any profile. A PST can have password protection whereas an OST cannot. Both have a default limit of 50 GB, which seems like a large amount until you come across a mailbox that has been growing since 2012.
When to Use an OST File
You generally don’t end up voting. When your mailbox is based on Exchange or Microsoft 365, Outlook creates the OST for you and looks after it as well; it also makes Outlook seem faster since clicking on a folder reads from your drive and avoids having to make a trip to the server.
When to Use a PST File
Create a copy when you want the data to be under your own control; people typically do so in order to free up space on their mailbox after it has reached its quota, to back up their data before swapping laptops, to transfer mail from one account to another, or to retain the outgoing employee’s mail for legal or human resources purposes.
I’ve watched a 15 GB mailbox stop throwing “storage full” warnings after the old years went into a PST. It took one afternoon.
What occurs when a Windows media file becomes damaged?
You would be surprised by how often this situation occurs. A company decides to retire its Exchange server, an administrator deletes a user, Outlook crashes when the file is large and the file ends up being corrupted. As a result, Outlook will no longer open it and your mail is then trapped inside.
The standard suggestion is to rebuild the profile and then get it to sync once more. That will work provided the mailbox still exists on the server; if it doesn’t, then the OST may be the last copy available and Microsoft does not provide a built-in method for opening it.
How to Recover OST Data When Outlook Won’t Open It
The situation that the BreviSoft OST to PST Converter deals with is this: it reads the OST file directly, even if the file is orphaned or damaged. You won’t need to have Outlook installed and there is no need for the old Exchange account.
You are given a preview of the folders and items before exporting, so that you can see exactly what is contained within them. You can choose to convert the entire file or apply a filter according to date or folder if you only want last year’s mail. Large files can be divided into smaller PST files, and if you’ve switched away from Outlook, you can import the data into Thunderbird and other email clients using the export formats that are supported.
If a company shuts down its old server and discovers twenty OST files on its staff laptops, it can convert each one and thus make all the mailboxes readable once again.
Conclusion
An OST is a working copy of your server mailbox and a PST is a file that you own; the majority of people never handle their OST and only produce a PST when they have a good reason.
Problems occur when an OST file loses its server; a new profile will not remedy this and merely waiting only increases the chance that the file will be lost or overwritten. Start by using the BreviSoft OST to PST Converter on a single file, look at the preview and then convert the rest.
