What are OST and PST files?
Microsoft Outlook stores data in OST and PST files format. Most people think Windows Outlook uses only PST format for storing data. However, that’s not true. There is also another file format that Outlook uses for almost similar purpose with few differences. It’s called OST.
Let’s take a look at the both files, their functions, and uses:
Like any other program, Outlook also stores the data somewhere within the database. It does so in both mail server and on your computer, including emails, contacts, tasks, calendar entries, settings and preferences and everything else. All these items are kept inside OST and PST files inside the profile folder.
OST files are used by Outlook when you are using Microsoft Exchange account. Outlook usually store items on the mail server, but to allow you to work even offline, it also creates the copies of your messages on your computer inside OST files. Therefore, OST is often considered an acronym for “Offline Storage Table” format.
PST on the other hand is used by Outlook when you use POP3, IMAP, and other web-based email accounts. You can also manually archive your data in PST files for backup reasons, but you can’t do that with OST files.
What is the difference between OST and PST files?
Another most common difference is that OST is always used when you set up your email account using Outlook connect for Outlook.com (formerly hotmail.com).
An archived PST file is also not subjected to mailbox size limits on your servers. By archiving data into PST file, you can free up space from your servers.
To put it more simply, offline folders (or OST files) are simply copies of your folders that are actually located inside your mailbox on the machine that is running the Microsoft exchange account. The use of OST file is similar to PST file – storing data – but it is used in different settings. It also allows you to work on your emails and other items offline. And as soon as the connection is restored, Outlook will automatically sync the changes made to OST with the mail servers.
You can also choose which folders are in sync with the OST. The servers by using ‘send/receive‘ options provided by Outlook.
If you don’t work offline a lot of time, it is often recommended to use the cached exchange mode of Outlook. It’s simply the lighter version of Offline OST files that you can use even when internet is connected. With the cached mode, you do not have to setup ‘send/receive groups’ at all. The client will itself synchronized any changes made with the servers when you were offline. It’s useful during minor connection interruptions, as opposed to working fully offline through OST files.
Where can you find these files?
To actually open the folder where these files are stored, follow the steps below:
Click ‘File’ –> ‘Account Settings’ –> ‘Account Settings’ –> Choose ‘Data Files’ tab
Click an entry and then choose “Open Folder Location” to automatically open the default database folder for your Outlook.
If the above steps don’t work for some reason, you can also manually go to this location through file explorer:
Windows Installation Drive –> Users –> ‘User’ –> AppData –> Local –> Microsoft –> Outlook. Make sure to check “Show Hidden files and folders” in folder settings because these folders are usually hidden.
One of the reasons to use archived PST files to store all your Outlook data is email migration. More precisely, when you are switching from Windows Outlook to some other client, like Mac Mail or Thunderbird, you might need these files for data conversion.
If you are looking to convert your PST files to some other format, try “PST Extractor Pro,” a handy Mac application for safe and quick data migration.