When you add an email account in Outlook, it automatically creates an Outlook data file based on the type of email account. For instance, if you sign in using an IMAP, Exchange, or Outlook.com account, Outlook creates an Offline Storage Table (.ost) file. However, when you add a POP account to Outlook, a Personal Storage Table (.pst) file is created. Let’s understand these Outlook data files in detail.
What is an OST File?
Offline Storage Table or OST file is also referred to as an Offline Folder file. It is a local copy of the mailbox on the server that allows users to access their mail items by using a MAPI email client, such as Outlook, even when the system is offline or on airplane mode.
Thus, OST helps users continue their work and use their email account. It enables them to draft or send emails and make other changes to the Outlook. These changes are saved locally in the OST file.
When the system connects to the internet, these local changes are synchronized with the mailbox on the server, and both local OST and mailbox on the server reach the same level of information.
OST File Location
OST file location varies based on the Outlook and Windows versions. By default, Outlook stores OST file at the following locations,
| Outlook Version | Windows Version | Location of OST |
| Outlook 2007
Outlook 2010 Outlook 2013 Outlook 2016 Outlook 2019 |
Windows 10 | C:\Users\YourProfileName\AppData\Local\Microsoft\Outlook\ |
| Outlook 2007 | Windows 7
Windows 8 |
C:\Users\%username%\AppData\Local\Microsoft\Outlook\ |
| Outlook 2010
Outlook 2013 Outlook 2016 Outlook 2019 |
Windows 7
Windows 8 |
C:\Users\%username%\Documents\Outlook File\ |
However, you can change the OST file location to a different folder or drive, including network storage. The location of OST file can be changed while setting up the Outlook account or after setting up the Outlook by editing the Registry files via Registry Editor or through Symbolic link (Symlink or Soft Link) method.
OST File Security
An OST file does not require any password-protection as it is encrypted by default. The encryption key is generated, by using the MAPIEntryID GUID, when Outlook is configured with the Exchange server. This key is saved on the mailbox server and local machine in the system’s registry. As the OST file is encrypted, it requires authentication.
Thus, whenever a user opens Outlook to access the mailbox data, the encryption key is matched from both ends. And access to the mailbox or synchronization starts only when the key matches. In case authentication fails, access to the OST file and the mailbox items is denied. Also, this makes OST safe from unauthorized access through any other Outlook profile.
OST File Size
Technically, a UNICODE OST file can grow as large as 4 PB. However, the default size limit for OST is set to 20 GB in Outlook 2007 and 50 GB in Outlook 2010 and later versions. Further, this OST file size limit can be increased or decreased by the organization as per the requirements via Registry Editor or Group Policies. You can also reduce or increase the OST size limit by using the sync slider under Cached Exchange Mode settings.
However, the OST file is just a cache copy of mailbox items stored on the server. Thus, there isn’t any problem in increasing the OST file size limit. Even if the OST file gets damaged due to large size, you can simply delete it and recreate it by signing in to Outlook again.
Advantages of OST Outlook Data File
Following are a few advantages of OST Outlook data file:
- Security
An OST file can be accessed through the original MAPI profile only. Thus, your data in OST remains protected.
- Offline Access
OST allows Outlook users to continue their work when the system is offline or there’s a problem with network and internet.
- Faster Access and Performance
OST allows users to access their mailbox items quickly. Even if the connection is unreliable, Outlook still lets you send or receive emails without any issue.
Disadvantages of OST Outlook Data File
Following are a few disadvantages of OST Outlook data files:
- Multiple OST Files Access is Denied
In Outlook, you can add multiple accounts but can access only one OST file at a time.
- OST Corruption
Although the OST file is resilient and stable for the most part, it may get damaged or corrupt due to virus or malware intrusion, synchronization errors, unreliable connection to network drive or internet, system crash, etc. However, if an OST file gets corrupt or you experience a problem with Outlook while accessing your emails, you can use the Inbox Repair utility (SCANPST.EXE) to fix errors and repair the OST file.
- Orphaned OST
When OST loses connection with the mailbox on the server, it is referred to as an orphaned OST file. This situation arises when the mailbox is deleted from the server, the alias is changed, the mailbox is transferred to a different database, or the Outlook profile is recreated. In such cases, the master ID is changed, which leads to an orphaned OST case.
IMPORTANT NOTE: Although the OST file is encrypted and protected by default, it can be accessed through an OST to PST converter software, such as Stellar Converter for OST. The software can read and convert OST to PST file without any authentication. Thus, allows any user to access and convert mail items stored in corrupt, inaccessible, or orphaned OST file to Outlook supported PST file.
About Personal Storage Table (PST) File
Personal Storage Table or PST file is also referred to as Personal Folder file. It stores a copy of your emails and other mailbox items on the local storage. PST is a commonly used Outlook data file format as it is portable and can be imported into any Outlook profile. It helps Outlook users backup their emails and mailbox contents easily and migrate them to a different Outlook profile, live Exchange, or an Office 365 account. r
PST File Location
You can find PST file at one of the following locations on your system based on Windows version:
| Windows Version | Location of PST |
| Windows 10 | C:\Users\YourProfileName\AppData\Local\Microsoft\Outlook\C:\Users\<username>\Roaming\Local\Microsoft\Outlook |
| Windows 7
Windows 8 |
C:\Documents and Settings\YourProfileName\Local Settings\Application Data\Microsoft\Outlook |
PST File Security
PST files are not usually secure as they are easily portable and can be accessed via Outlook, live Exchange, or Office 365 accounts. Any user can import a PST file into an Outlook account and access the data. Although, you can password-protect the PST files to protect them from unauthorized import or access.
Also, as the size of PST file grows larger, it becomes more unstable and may impact Outlook performance. This may also lead to damage to the PST file and cause corruption that can result in permanent data loss. However, such situations can be avoided by splitting the PST file with the help of a PST repair software. You may also export multiple PST files via Outlook wizard and then open them in Outlook to access emails and mailbox items.
Additionally, if the PST Outlook data file is stored and accessed by Outlook via a network location, it may increase the chances of damage to the PST file if the connection is not reliable or the system suffers from frequent disconnection.
PST File Size
Earlier Outlook versions had a 2 GB file size limit for PST. However, this was changed to 20 GB with Outlook 2003 and 2007. Now a UNICODE Outlook PST file can technically grow to a size as large as 4 PB. However, similar to OST, the default PST size limit is set to 50 GB that can be changed as per the preference and requirements of the user.
Advantages of PST Outlook Data File
Following are a few advantages of PST Outlook data file:
- PST Outlook data file format is used for backup and migration purposes
- One can easily open, access, and import PST files in any Outlook account
- They can be password-protected to avoid unauthorized access
- OST users can export old mailbox content to PST format and reduce their OST mailbox size
- Data stored in local PST can be accessed quickly and thus, helps improve Outlook performance
- Helps move data from Exchange or Outlook account to Office 365
Disadvantages of PST Outlook Data File
Following are some disadvantages of PST Outlook data files:
- PST files can’t store multi-gigabyte mailbox content as they become unstable and may get corrupt, leading to data loss
- Common issues, such as sudden system shutdown, power outage, PC crash, may turn PST file inaccessible
- Although PST Outlook data files can be password-protected, the password can be removed by using tools easily available on the internet
Outlook Data File (OST & PST) Backup and Recovery
Outlook data files may get damaged or corrupt due to problems with the system, storage media, malware or virus intrusion, PC crash, etc. Thus, it’s important to know how you can protect your data stored in Outlook data file in case of corruption and restore lost data.
OST Backup and Recovery
You can back up the data stored in OST file through the Outlook Import Export wizard. The wizard helps you to back up the emails and other mailbox items from the OST Outlook data file to PST format that you can open, access, and import in any Outlook profile.
To access inaccessible OST files, you will require an OST to PST converter software. The software can also help you retrieve and backup mailbox data from an inaccessible or orphaned OST file. It also helps recover deleted mailbox items, such as emails, attachments, contacts, tasks, etc. from any OST file.
PST Backup and Recovery
Generally, PST files are not backed up. Also, as mentioned earlier, they turn unstable as their size grows larger which may lead to corruption. Once damaged, you may fix them with the help of SCANPST.EXE (Inbox Repair Utility).
However, if the utility fails, then you have to rely on an OST/PST repair and converter software, such as Stellar Toolkit for Outlook to fix the problem with OST or PST file and restore mail items. The toolkit is an all-in-one package for Outlook users and administrators. It features 8 different tools to fix various issues with the Outlook and Outlook data files i.e., OST and PST.
- Stellar Repair for Outlook Technician
- Stellar Converter for OST Technician
- Stellar Splitter for Outlook
- Stellar Compactor for Outlook
- Stellar Merge Mailbox for Outlook
- Stellar Deduplicator for Outlook
- Stellar Undelete Email for Outlook
- Stellar Password Recovery for Outlook
This toolkit features options to repair corrupt or damaged PST file and to convert an inaccessible, orphaned or damaged OST file to PST format.
It can help fix large-sized OST or PST without any risk of data loss. In fact, the toolkit recovers lost or deleted mail items during the OST to PST conversion or PST repair process. The toolkit also provides option to split, compact, or merge PST, which helps optimize Outlook performance and reduces risk of Outlook data file corruption. You can buy it from here.
Hope this article helps you understand OST and PST Outlook data files. However, if you have any queries or need help, feel free to leave a comment.