Outlook OST File Too Large to Open: How to Reduce It?

Summary: From a technical perspective, the OST file serves as a mirror of your mailbox data. This data gets accumulated over a period of time and triggers an error, “Outlook OST File Too Large”. The error appears when the OST file breaches its maximum supported size threshold. It’s 50 GB for Outlook 2010 and 20 GB for Outlook 2007. A large OST file also leads to file corruption, making the Outlook data suffer. Continue to read the blog to learn more about this error and ways in which we can fix it.

Factors Causing “OST File Too Large” Outlook Error?

If too much data is being stored in the mailbox, or it is not cleaned up regularly, it increases the OST file size. Have a look at the factors causing it:

• The mailbox contains too many email messages accumulated over a period of time.
• Attached media, like photos, videos, and documents, are increasing the OST file size.
• Microsoft Outlook is syncing several shared mailboxes and folders at once. This enlarges the OST file size.
• Cached Exchange Mode stores years of emails locally for offline access and syncs them to the OST file.
• Additional Outlook items, such as tasks, notes, and calendar data, are adding to the OST size. 

Issues Caused by an Oversized Outlook OST File in Outlook

Below are the common issues that are caused by an oversized Outlook OST file:

• Sluggish, Unresponsive Outlook Performance: With an oversized OST file, Outlook struggles to load mailbox data.
• Mail Synchronization is Delayed: When the OST file hits the storage limit, Outlook will not be able to pull new emails from the server. 
• Outlook Search is not showing accurate results: An oversized OST file prevents MS Outlook from maintaining the search index. 
• Frequent Outlook Crashes: If Outlook repeatedly crashes, it can hamper the all-day business operations, including managing client communications. 
• Risk of Outlook Mailbox Corruption: A large OST file can corrupt the entire local database. 

Troubleshooting Methods to Fix “Outlook OST File Too Large” Error

Look at the following solutions that can fix the Outlook oversized OST file error. Each of the solutions is explained in detail. 

Method 01: Remove Unnecessary Emails

Simply remove the unwanted emails from the Inbox, Sent Items, and Deleted Items folders. This helps free up the space and improves Outlook performance.

1. In MS Outlook, go to the desired mailbox and select the unnecessary emails.
2. Then, press the Delete button. 
3. After that, go to the Deleted Items folder and choose Empty Folder.
4. Next, restart MS Outlook.

Method 02: Archive Old Emails 

If the Outlook OST file too big, users can try archiving the old emails to reduce the size of their OST file. When these emails are archived, they are moved to a separate PST file.

1. Open the Outlook application and press File.
2. Then, select Tools > Archive and choose the folder you want to archive.
3. Next, enable Archive this folder and all subfolders, and select a location to save the archived file.
4. After that, click on Ok and restart Outlook.

Method 03: Compact the OST File

Users can compact their OST file in Microsoft Outlook if the OST file is too large. It can help remove the space left behind after deleting attachments or emails. 

1. First, launch the Outlook application.
2. Then, go to the File tab and select Account Settings > Account Settings.
3. Open the Data Files tab and choose the desired OST file.
4. Next, click on Settings > Advanced > Outlook Data File Settings.
5. After that, press the Compact Now button and restart Outlook.

Method 04: Mailbox CleanUp in MS Outlook

The Mailbox Cleanup feature in Microsoft Outlook rectifies the user query “my OST file is too big”. It helps identify and remove unnecessary items. 

1. In MS Outlook, head to the File tab and click on Tools.
2. Next, choose Mailbox Cleanup > View Mailbox Size.
3. Now, locate large emails using Find items older than or Find items larger than.
4. After that, delete those unnecessary emails and click Empty next to the Deleted Items folder.
5. Finally, close the Mailbox Cleanup window and restart Outlook. 

Method 05: Reliable Tool to Fix Outlook OST File Too Large Error

The oversized OST files are a headache for many service providers. This is where the OST Splitter Tool helps. It gives the IT teams a purpose-built solution that cuts out the downtime, risk, and manual effort. The tool splits the oversized OST file into structured files without altering the underlying data. With this tool, users can significantly reduce the turnaround time while keeping the service delivery efficient. 

Simple steps to fix OST file too large Outlook error:

1. Download and run the tool as an administrator.
2. Then, click on the Add File option, browse the oversized OST file, and press Open. Click Next.
3. After that, expand the folder tree, select the folders, and choose the desired Splitting option. 
4. Next, select the PST file size and choose the path to save the file.
5. Finally, click on the Split button to begin the process.

Conclusion

A large OST file may lead to synchronization issues and make mailbox data inaccessible for Outlook and Exchange users. As a result of this, many users look for manual methods to fix the “Outlook OST File Too Large” error. The users can try different methods to fix this issue to improve Outlook’s performance. Alternatively, the best solution is to use a professional OST Splitter Tool to split the oversized OST file.

Note: Also, users can choose to open OST file without Outlook to verify the size of their file.

Frequently Asked Questions