Outlook OST File Location Explained (Windows & Mac)

Microsoft Outlook is a widely used email client for both individual and business communication. One integral part of Outlook’s functionality is its ability to store mailbox data locally using OST files. These Offline Storage Table files allow users to access their email, calendar, tasks, and more even without an internet connection. However, understanding where these OST files are located can be a bit confusing—especially since the file paths differ between Windows and Mac systems and may vary based on Outlook versions and settings.

TLDR (Too long, didn’t read)

OST files are local copies of mailbox data generated by Microsoft Outlook when using an Exchange, Microsoft 365, or IMAP account. On Windows, they are typically stored in a hidden folder under your user profile, while on Mac, the folder structure differs and uses the Outlook for Mac database methodology. Knowing the OST file location can help in backups, migrations, or troubleshooting issues such as profile corruption or drive space concerns.

What is an OST File?

An OST (Offline Storage Table) file is a locally stored file on your computer that mirrors the mailbox contents stored on Microsoft Exchange servers or other mail servers like Microsoft 365 or IMAP. This allows users to work on their emails offline, and changes are synchronized the next time Outlook connects to the internet.

Here are the key characteristics of OST files:

Offline Access: Enables use of emails, calendars, contacts, etc., even without internet connectivity.
Synchronization: Any changes made offline are automatically synced when the user is online.
User-Specific: OST files are specific to a configured Outlook profile.

OST File Location in Windows

On Windows, Outlook OST files are stored in a default directory path unless manually changed by the user. The typical default path is:

C:\Users\username\AppData\Local\Microsoft\Outlook\

Here’s a breakdown of locations based on Outlook versions and scenarios:

Default OST File Locations by Outlook Version (Windows)

Outlook 2019/2016/2013:
C:\Users\username\AppData\Local\Microsoft\Outlook\
Outlook 2010 and earlier:
C:\Users\username\AppData\Local\Microsoft\Outlook\ or
C:\Documents and Settings\username\Local Settings\Application Data\Microsoft\Outlook\

To access this folder quickly, users can type %LOCALAPPDATA%\Microsoft\Outlook\ into the File Explorer address bar.

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How to Locate OST File from Within Outlook (Windows)

For those unsure where their OST file is stored, Outlook provides a simple way to find it:

Open Outlook.
Go to File → Account Settings → Account Settings.
Select the appropriate email account and click Data Files.
In the popup window, the location of the OST file will be displayed as a path. You can select and open it directly.

OST File Location in Mac

Unlike Windows, MacOS does not use separate *.ost or *.pst files for individual emails. Instead, it stores all mailbox data as part of the Outlook profile in database format. The data location is buried within the user’s Library directory.

Default Outlook Data Location in Mac

/Users/username/Library/Group Containers/UBF8T346G9.Office/Outlook/Outlook 15 Profiles/

This path may vary slightly depending on your Outlook version. Within this profile directory, you’ll find the full database that handles emails, calendars, and even cached attachments.

Steps to Locate Outlook Data on Mac

Open Finder.
Click on Go in the top menu, then choose Go to Folder…
Type: ~/Library/Group Containers/UBF8T346G9.Office/Outlook/
Press Return to access the data folder.

Since Outlook for Mac does not create OST files the way Windows does, you won’t find individual *.ost files. Instead, look for data inside the Main Profile (often named “Main Profile”) folder, where email and other information are stored in various cache and sqlite database files.

Why Knowing OST File Location Matters

Understanding where the OST file is stored can be helpful for multiple reasons:

Troubleshooting: Corruption in the OST file can lead to Outlook crashing or becoming unresponsive.
Backup & Restore: While OST files are not typically backed up, if you use .pst files or convert OST to PST, you’ll need to know the location.
Freeing Disk Space: OST files can become large—sometimes many GBs in size—so knowing where they are stored helps in clearing unnecessary cache.
Profile Management: Deleting or relocating OST files may be necessary when recreating Outlook profiles or cleaning up accounts.

How to Change OST File Location (Windows)

Technically, Outlook does not offer a straightforward way to change the OST file location. However, advanced users can relocate it using symbolic links or by changing registry settings:

Create a new Outlook profile and choose a new location for data files during setup.
Use mklink to create a symbolic link from the default location to your desired folder.

Note: Changing OST file locations this way can cause issues if not done correctly—always back up your data first.

Understanding OST vs PST Files

Some users confuse OST files with PST files, but they serve different functions:

OST (Offline Storage Table): Automatically created by Outlook for Exchange, Microsoft 365, and IMAP accounts. Not usually portable.
PST (Personal Storage Table): Used for archiving and manually backed up or shared data. Fully portable and can be imported into any Outlook client.

Conclusion

Locating the OST file on Windows or understanding the data storage format on macOS can be essential for anyone administering Outlook, troubleshooting issues, or managing disk space. While Windows offers more conventional paths to locate and manage OST files, Mac uses a different system with database-like profiles. Whichever platform you’re using, this knowledge can help you maintain, recover, or transition Outlook profiles more efficiently.

Frequently Asked Questions (FAQ)

Q: What is an OST file used for?: A: OST files store a copy of mailbox data, allowing Outlook to function offline and sync changes when reconnected.
Q: Can I open an OST file without Outlook?: A: Not directly. OST files are tied to a specific Outlook profile. You can use third-party tools to convert or view them outside Outlook.
Q: Is it safe to delete the OST file?: A: Yes, but only if you know what you’re doing. Outlook will recreate the OST file when you reopen and connect to your account, but unsynced changes might be lost.
Q: Can I move the OST file to another drive?: A: Yes, but it requires technical steps like changing registry entries or using symbolic links, which should be performed with caution.
Q: Does Mac Outlook use OST files?: A: No, Outlook for Mac uses a database format stored under Group Containers. It does not create a separate OST file like Windows does.
Q: Are OST files encrypted?: A: OST files may be encrypted depending on your Outlook and Exchange settings. They’re not meant to be shared or transferred between systems.