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How to resolve the issue “application pauses if you have a large outlook data file”?

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    Summary: If you have a large Outlook data file (OST), you may experience application pauses, performance issues, and other problems with Outlook. To resolve such issues, the best option is to reduce the size of the Outlook OST file. This article discusses different ways to reduce the OST file size.

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    Offline Storage Table (OST) file is created by Microsoft Outlook, when it is configured with Exchange or IMAP account, to store all the online mailbox data on the local system. However, Microsoft has defined a particular limit for the OST file size. For Outlook 2013, 2016, 2019, and 2021, OST files can hold up to 20 GB of data. The maximum file size that can be extended is 50 GB (gigabytes). If the file size reaches the defined limit, you may experience performance issues with Outlook, such as application pauses, slow Outlook performance, problems receiving and sending emails, and even file corruption. Below, we’ll discuss ways to reduce the OST file size to prevent and resolve such issues.

    How to Resolve the Application Pauses Issue Due to Large Outlook Data File?

    To avoid and resolve Outlook pauses and other issues due to large offline data files (.ost), the best solution is to reduce the file size of offline OST files. Here are some ways to reduce it.

    Solution 1: Archive Outlook Items

    You can archive old or unwanted items to reduce the mailbox (OST) size. Here are the steps to archive items in Outlook 2016, 2019, and 2021.

    • Open Outlook and go to the File menu.
    • Select Tools from the left panel and select Clean Up old items.
    • Now, in the Archive this folder and all subfolders option, choose the folder you want to archive.
    • You can also opt for the entire mailbox to archive. Choose the email address for the same.
    • Under Archive items older than an option, choose the Date Range.
    • You can also check the Include items with “Do not AutoArchive” checked box.
    Archive option for Import & Export wizard
    • After that, click on Browse to save the archived mailbox and press the OK tab.

    Solution 2: Auto-Archive Old Emails

    Microsoft Outlook has a great feature that automatically archives old emails. To enable this feature, follow the given steps:

    • Run Outlook and select the File option in the ribbon.
    • Choose Options from the left panel and click Advanced.
    • Under Auto-Archive, select the auto-archive setting and hit the OK tab.
    • Click the Run AutoArchive every n day’s box and specify how often you want Outlook to run AutoArchive.
    • After the archive process is completed, an archive folder will appear in your Outlook account.

    Solution 3: Turn off Cached Exchange Mode for Delegate Mailbox

    Delegate Mailbox or Shared Folder is one of the common features in MS Outlook used by working professionals. If you’ve enabled the caching of the delegate mailbox or shared folder, then it can significantly add to the size of the OST file. You can disable the Cached Exchange Mode for the shared mailbox (delegate mailbox) to prevent the size of the OST file from exceeding the limit. The steps are as follows:

    1. Start MS Outlook and go to the File option in the ribbon.
    1. Select Account Settings > Account Settings and click on your Exchange account. Then, click on Change and go to More Settings.
    1. Select Cached Exchange Mode Settings, select Advance tab, and uncheck the Download Shared Folder or Download Public Folder Favorites option.
    2. Click Apply and then OK.
    1. Restart your Outlook.

    Other Solutions to Deal with Large OST Files

    • Maintain Items per Folder Limit: Microsoft has set a maximum limit of 100,000 items per folder in Outlook 2019, 2016, 2013, and 2010. If this limit exceeds, you can start experiencing performance problems with Outlook. Therefore, it is advisable to maintain a reasonable number of items per folder to ensure optimal performance of Outlook.
    • Delete Expired Items: You can enable this option to delete expired messages from email folders. This feature is available under options.
    • Move Old Items: This Outlook feature allows you to move old emails and other items to archived PST files. You can save this archived PST file at the desired location.
    • Permanent Deletion: Applying this setting to the Outlook items will permanently delete mailbox items without archiving.    


    Large or oversized OST files can cause application pauses, performance issues, and other problems with Outlook. Large OST file is also prone to corruption and damage. To manage or reduce the size of large Outlook offline (.ost) files, we have listed different ways in this article. In case, the OST file becomes corrupted or inaccessible due to its large size, you can convert the OST into PST by using a professional OST to PST converter tool, such as Stellar Converter for OST. This tool can easily convert large-sized offline (.ost) files into PST. The technician edition of this tool can also split and compact large converted OST file.

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    About The Author

    Eric Simson linkdin

    Eric Simson is an Email Platform Consultant and is associated with Stellar Data Recovery from last 6 years. He writes about the latest technology tips and provides custom solutions related to MS Outlook, MS Exchange Server, Office 365, and many other Email Clients & Servers.

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