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If you have ever used Outlook with an Exchange, Microsoft 365, or IMAP account, you have probably heard of an OST file without even realizing it. For most users, OST files go completely unnoticed until something goes wrong with your Outlook, like Outlook won’t open, a file suddenly becomes inaccessible, your account gets removed, or data disappears from your mailbox. This is where users start searching: What exactly is the OST file? Why can’t I open it normally?
What is an OST File in Outlook?
Offline Storage Table (OST) file is associated with your Outlook account which enables the user to access, read, delete, manage, and compose emails even in offline mode. Outlook creates this file automatically when you integrate Outlook with an Exchange or Office 365 account.
OST files are highly secure, encrypted with MAPIEntryID GUID key, and hard to corrupt. Further, the size limit is up to 50 GB by default in Outlook 2013 to the latest versions.
Where OST Files Are Stored on Your System?
Knowing the location of your OST file can help in various situations. You can find the OST file linked to your Outlook at:
| Outlook Version | Windows Version | Default Location |
|---|---|---|
| Outlook 2000 Outlook 2003 Outlook 2007 |
Windows XP | C:\Documents and Settings\Username\Local Settings\Application Data\Microsoft\Outlook |
| Outlook 2007 | Windows Vista Windows 7 Windows 8 Windows 10 Windows 10 |
C:\Users\User\Name\AppData\Local\Microsoft\Outlook |
| Outlook 2010 | Windows XP | My Documents\Outlook Files |
| Outlook 2010 | Windows Vista Windows 7 Windows 8 Windows 10 Windows 11 |
C:\Users\\Documents\Outlook Files |
| Outlook 2013 Outlook 2016 Outlook 2019 Outlook 365 |
Windows Vista Windows 7 Windows 8 Windows 10 Windows 11 |
C:\Users\admin\AppData\Local\Microsoft\Outlook |
In case you have changed the OST file location in the past or can’t find it at the default location, then follow the below-mentioned steps to figure out the OST file’s current location.
- Open Outlook and go to File, then click on the Account Settings option and again click on Account Settings.
- Hit the Data Files tab and select the OST file, then click on the Open File Location
- You will be redirected to the location where your OST file is currently stored.
Common Problems with OST Files
Issues without OST files often cause Outlook to freeze or crash. Here are some common problems which mostly users face with OST files:
- OST files grow rapidly, which can lead to issues like slow Outlook performance, Outlook stuck on loading profile, etc.
- Abrupt shutdown of Outlook, faulty add-ins, large OST file size, etc., cause corruption in Outlook data files.
- Many users choose to encrypt their Outlook data files with passwords to add an extra layer of security. And sometimes, users forget the password, leading to inaccessible OST files.
- Any synchronization issues between OST and Exchange Server breaks the link between local data and Exchange that leave the folder empty or outdated.
User’s Query Answered: Can I Open an OST File Directly?
Unfortunately you cannot directly open an OST file in Microsoft Outlook or another email client. Outlook does not provide a direct way to open the OST file. Further, an OST file is strictly tied to the Outlook profile it was originally created with. To open and access its data, you will need to use a dedicated OST Viewer tool, as there are no built-in Windows viewer tools for OST files.
Final Verdict
An OST file is basically Outlook’s offline backup of your mailbox. You can easily work with OST files even when you are offline. Once you are back online, Outlook syncs everything to the server so nothing gets missing. To avoid problems, keep your Outlook updated, don’t let OST grow too large, and make sure Outlook closes properly.
Moreover, in case your OST file becomes corrupted, you can repair damaged OST files or even look to convert OST to PST with a dedicated OST to PST Converter tool. Get in touch with our experts to know more about the conversion.
Frequently Asked Questions
Yes, you can read, reply, and organize emails offline with OST files.
Yes. The size limit is 50 GB for Outlook 2010-2019 and 100 GB for Outlook 365.
Yes, an OST file can get corrupted. To fix such issues, you need to repair corrupted OST files.
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