Why is OST File So Large? Causes & Reduce OST Size
Microsoft Outlook is used for communication and data management in both business and personal environments. The OST files are created when we are using Outlook with an Exchange Server, IMAP account or Microsoft 365. The files store emails, attachments, calendar, contacts, tasks, and other mailbox items. This file stores a synchronised copy of the mailbox data locally, which enables users to work on it without an internet connection, and thus automatically syncs with the changes later. Over time, the emails accumulated, which makes the OST files oversized. Thus, it becomes tricky to manage the oversized OST files, and thus, corruption in any of these will result in Outlook data suffering. In this article, we will learn about “Why is OST file so large?” and get the best solution from here.
Why is My OST File so Large? What are the Common Causes
Several types of factors, by and large, are responsible for the expansion of OST files. The largest part of it is described here:
- Large Volume of Emails and Attachments: It would be fair to say that the biggest cause of the ever-growing OST files is, by far, the email attachments. These attachments can be in the form of PDF files, videos, spreadsheets, or presentations. The email folders – Inbox, Sent Items, and Deleted Items – tend to store thousands of messages as time goes by.
- Shared Mailbox or Additional Account: The data of the shared mailbox and the public folders to which you have access via Outlook are also downloaded by Outlook, and that is why the size of the OST file is rapidly increasing.
- Multiple Calendars and Contacts Lists: Huge Calendars, especially those with Attachments, meetings, or shared, take up a lot of space, thus making the OST file so large.
- Items not Clearly Deleted: There is a catch that after deleting an email from the Inbox, it still appears in the Deleted Items folder until one manually empties that folder. Junk Mail also puts on weight, and that is one of the reasons why the size of OST files is so large.
- Outlook Add-ins and Plugins: Third-party integrations, such as CRM tools, can expand the OST file size by storing the cache data. This could also be the reason why the OST file is so large.
- Corruption or Synchronisation Errors: If the synchronisation fails repeatedly, Outlook keeps multiple copies of duplicate items, increasing the OST size unexpectedly.
How to Know the Size of the OST Files
- Launch Outlook.
- Go to File > Account Settings > Account Settings.
- Select the email account, and click on Data Files.
- Choose the OST file, and click on Open File Location.
- Right-click the OST File and select Properties.
It shows the mailbox folder sizes and helps you locate the folders that consume the most space.
How to Reduce the Size of the OST Files: Fix “Why is the OST file so large?”
The problem of the large file size of Outlook can be resolved by employing the following measures, which are also quite effective for enhancing the overall Outlook functioning:
Delete Unnecessary Emails & Attachments
Go through each of the folders like Inbox, Sent Items, Delete Items, Drafts, Spam/Junk folder, and manually delete the emails that are stored there. This would fix the issues with the OST file so large.
Remove large attachments; or, you may want to move them to the local directory, and then take them out of the emails. If you want to make this task simpler, then get the Email Attachment Remover.
Enable auto clear
Steps to Enable auto clear delete items:
- Go to File.
- Select Options.
- Choose Advanced.
- Under Outlook Start and Exit, enable Empty Delete Items folder upon exiting Outlook.
Reduce the Cached Mailbox Size
- Go to File > Account Settings.
- Select Account > Change.
- Under Mail, keep offline.
- Restart Outlook.
This removes older items from the OST files but keeps them in the server. This way you can resolve the issue related with “OST file is large”.
Compact OST Files
You can try compacting the files, as even after deleting the items, Outlook does not shrink the file automatically.
- Go to File > Account Settings
- Select Email Account > Data Files
- Choose the OST file > Settings.
- Click Compact Now
Archive Old Emails
We can use the archive method to work on the “Why is the OST file so large?” question. Use Outlook’s Archiving features:
- File > Tools > Clean up old Items.
- Move items older than 6 months or 1 year to a PST archive file.
Repair OST File
If you suspect the OST file so large issue is due to corruption, rebuild the OST.
- Close Outlook.
- Navigate to the OST file and rename the extension.
- Restart Outlook.
- It creates a fresh OST and re-downloads the mailbox.
Or use the SCANPST.exe repair tool.
Use the Tool to Fix “Why is the OST File So Large?”
To reduce the size of the Outlook OST files, use the OST File Splitter. As the name suggests, it can split the large file into a desired size for the users. The users are enabled to select the size limit that they prefer for splitting in accordance with their system performance needs. The tool guarantees that the emails, the files, the contacts, and so on, are kept safe and that the users can access them after the division. The performance of Outlook is thereby enhanced, and the problems of file corruption are avoided at the same time.
How to Prevent the OST File from Accumulating
- Clean the Mailbox Weekly.
- Remove large attachments from Outlook.
- Compact OST files monthly or in 3 -4 weeks.
- Limit shared mailbox download.
Conclusion
A large OST file usually causes issues with the mailbox size, attachments, cached synchronisations, or unused deleted items. Oversized OST files slow down Outlook performance and lead to corruption. The article has given all the solutions like deleting unnecessary data, limiting cache size, enabling archive settings, and repairing the files when required, significantly reducing the OST size and optimising the Outlook performance.