{"id":63462,"date":"2020-08-27T11:41:29","date_gmt":"2020-08-27T11:41:29","guid":{"rendered":"https:\/\/www.stellarinfo.com\/blog\/?p=63462"},"modified":"2026-05-07T05:35:37","modified_gmt":"2026-05-07T05:35:37","slug":"compact-outlook-ost-file","status":"publish","type":"post","link":"https:\/\/www.stellarinfo.com\/blog\/compact-outlook-ost-file\/","title":{"rendered":"How to Compact OST File in Outlook?"},"content":{"rendered":"<?xml encoding=\"utf-8\" ?><?xml encoding=\"utf-8\" ?><p>In Outlook, to compact the OST file, open the <strong>Account Settings &gt; select the Data Files option &gt; file &gt; Settings<\/strong>, and select the Compact Now option. This process removes White Space &ndash; created after deleting the mail items. This will reduce the file size and help improve your Outlook performance, and also prevent other issues associated with large data files.<\/p><p>Read this guide to know the detailed process to compact OST file in Outlook.<\/p><h2 class=\"wp-block-heading\" id=\"what-is-an-offline-storage-table-(ost)-file?&nbsp;\"><strong>What is an Offline Storage Table (OST) File?&nbsp;<\/strong><\/h2><p>An OST &ndash; Offline Storage Table &ndash; file is a cached copy of your Exchange mailbox. It stores all your mailbox items on your local device. You can access these items even when you are not connected to the server.<\/p><h2 class=\"wp-block-heading\" id=\"what-causes-ost-files-to-grow-in-size?\"><strong>What Causes OST Files to Grow in Size?<\/strong><\/h2><p>Your OST file can grow in size due to the following factors:<\/p><ul class=\"wp-block-list\">\n<li>Continuous emails accumulation<\/li>\n\n\n\n<li>Large email attachments<\/li>\n\n\n\n<li>Synchronization of data and metadata in the background<\/li>\n\n\n\n<li>Lots of white space (unused space after mail items deletion)&nbsp;<\/li>\n\n\n\n<li>Downloading of shared mailboxes and public folders data<\/li>\n\n\n\n<li>Cached Mode is enabled&nbsp;&nbsp;<\/li>\n<\/ul><h2 class=\"wp-block-heading\" id=\"what-happens-when-an-ost-file-becomes-large?\"><strong>What Happens When an OST File becomes Large?<\/strong><\/h2><p>When the OST file becomes too large or oversized, it can lead to problems like:<\/p><ul class=\"wp-block-list\">\n<li>Slower Outlook performance<\/li>\n\n\n\n<li>Synchronization errors<\/li>\n\n\n\n<li>Send\/receive errors<\/li>\n\n\n\n<li>Outlook freezing or not responding issue<\/li>\n<\/ul><h2 class=\"wp-block-heading\" id=\"what-is-the-maximum-ost-file-size-limit?\"><strong>What is the Maximum OST File Size Limit?<\/strong><\/h2><p>The maximum OST file size limit depends on your Outlook version. As per the &nbsp;<a href=\"https:\/\/learn.microsoft.com\/en-us\/previous-versions\/troubleshoot\/outlook\/file-size-limits-of-pst-and-ost-files-are-larger\" target=\"_blank\" rel=\"noreferrer noopener nofollow\">Microsoft document<\/a>, the file size limits are 50 GB in Outlook 2010 and later versions. This <a href=\"https:\/\/www.stellarinfo.com\/blog\/increase-ost-file-size-microsoft-outlook\/?srsltid=AfmBOorgirgjDDtXoPkw4nRnJTEsDpFLb1LduGsZqoJaXQ2cgfojU97g\">limit can be increased<\/a> &nbsp;via registry or Group Policy if your OST hits its default size limit.<\/p><p>The table below shows the default and maximum configurable size limits for OST files across different versions of Outlook:<\/p><figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><tbody><tr><td><strong>Outlook Version<\/strong><\/td><td><strong>Default OST Size Limit<\/strong><\/td><td><strong>Maximum Configurable Size (Registry)<\/strong><\/td><td><strong>Recommended Compact Frequency<\/strong><\/td><\/tr><tr><td><strong>Outlook 2007<\/strong><\/td><td>20 GB<\/td><td>Not applicable<\/td><td><strong>Not applicable (no registry override)<\/strong><\/td><\/tr><tr><td><strong>Outlook 2010 \/ 2013<\/strong><\/td><td>50 GB<\/td><td>100 GB<\/td><td><strong>Every 2&ndash;3 months<\/strong><\/td><\/tr><tr><td><strong>Outlook 2016 \/ 2019 \/ 2021 \/ Microsoft 365<\/strong><\/td><td>50 GB<\/td><td>100 GB<\/td><td><strong>Monthly for heavy users<\/strong><\/td><\/tr><\/tbody><\/table><\/figure><h2 class=\"wp-block-heading\" id=\"what-happens-when-ost-becomes-large?\"><strong>What Happens When OST Becomes Large?<\/strong><\/h2><p>When your OST file becomes too large, Outlook may start showing performance issues like slow startup, delayed send\/receive operations, sync failures, etc. In some cases, you may also see warnings like <a href=\"https:\/\/www.stellarinfo.com\/blog\/how-to-fix-error-your-mailbox-is-almost-full-in-outlook-365\/\">Outlook 365 mailbox almost full<\/a>, which indicates that mailbox maintenance is required.<\/p><h2 class=\"wp-block-heading\" id=\"why-should-you-compact-the-ost-file?\"><strong>Why should you Compact the OST File?<\/strong><\/h2><p>Here are some benefits of compacting the OST file:<\/p><p><strong>Reclaims unused space left after deleting emails and other items<\/strong><\/p><p>Deleted emails leave behind unused space inside the OST file. Compacting removes this white space and helps reduce the file size.<\/p><p><strong>Improves Outlook startup, shutdown, and search performance<\/strong><\/p><p>A smaller OST file helps Outlook open, close, and search emails faster with fewer delays.<\/p><p><strong>Helps prevent sync errors and send\/receive failures<\/strong><\/p><p>Large OST files can cause syncing problems with the mail server. Compacting improves synchronization and reduces send\/receive errors.<\/p><p><strong>Reduces the risk of OST file corruption<\/strong><\/p><p>Oversized OST files are more likely to get damaged. Compacting keeps the file manageable and improves Outlook stability.<\/p><h2 class=\"wp-block-heading\" id=\"what-are-the-methods-to-compact-ost-file-in-outlook?\"><strong>What are the methods to Compact OST File in Outlook?<\/strong><\/h2><p>Below, we have explained four methods that you may follow to compact the Outlook OST file:<\/p><h3 class=\"wp-block-heading\"><strong>Method 1. Use &lsquo;Compact Now&rsquo; Option in Outlook<\/strong><\/h3><p>Outlook compacts the OST file by default when the &ldquo;unused space&rdquo; (white space) reaches 20% of the file size. However, you can also manually compact the OST file using the built-in option.<\/p><blockquote class=\"note_alert\">\n<p><strong><em>Note:<\/em><\/strong><em> Before compacting the OST file make sure empty the Deleted Items folder first. Compact Now only removes white space from already-deleted items &mdash; compacting does nothing if Deleted Items is full.<\/em><\/p>\n<\/blockquote><p>To do this:<\/p><ul class=\"wp-block-list\">\n<li>Open Outlook.<\/li>\n\n\n\n<li>Navigate to&nbsp;<strong>File.<\/strong><\/li>\n\n\n\n<li>Select<strong> Account Settings&nbsp;&gt; Account Settings.<\/strong><\/li>\n\n\n\n<li>Click on the&nbsp;<strong>Data Files<\/strong>&nbsp;tab.<\/li>\n<\/ul><div class=\"wp-block-image\">\n<figure class=\"aligncenter size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"619\" height=\"508\" src=\"https:\/\/www.stellarinfo.com\/blog\/wp-content\/uploads\/2020\/08\/Outlook-data-file.png\" alt=\"Click on the&nbsp;Data Files&nbsp;tab\" class=\"wp-image-63464 apply-gradient-on-post-images\" srcset=\"https:\/\/www.stellarinfo.com\/blog\/wp-content\/uploads\/2020\/08\/Outlook-data-file.png 619w, https:\/\/www.stellarinfo.com\/blog\/wp-content\/uploads\/2020\/08\/Outlook-data-file-300x246.png 300w\" sizes=\"auto, (max-width: 619px) 100vw, 619px\" \/><\/figure>\n<\/div><ul class=\"wp-block-list\">\n<li>Select the OST data file that you want to compact.<\/li>\n\n\n\n<li>Then click&nbsp;<strong>Settings &gt;&nbsp;Advanced.<\/strong><\/li>\n\n\n\n<li><strong>&nbsp;<\/strong>Select <strong>Outlook Data File Settings&hellip;<\/strong><\/li>\n<\/ul><div class=\"wp-block-image\">\n<figure class=\"aligncenter size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"345\" height=\"425\" src=\"https:\/\/www.stellarinfo.com\/blog\/wp-content\/uploads\/2020\/08\/use-cached-exchange-mode.png\" alt=\"Select Outlook Data File Settings\" class=\"wp-image-63465 apply-gradient-on-post-images\" srcset=\"https:\/\/www.stellarinfo.com\/blog\/wp-content\/uploads\/2020\/08\/use-cached-exchange-mode.png 345w, https:\/\/www.stellarinfo.com\/blog\/wp-content\/uploads\/2020\/08\/use-cached-exchange-mode-244x300.png 244w\" sizes=\"auto, (max-width: 345px) 100vw, 345px\" \/><\/figure>\n<\/div><ul class=\"wp-block-list\">\n<li>Click onthe<strong> Compact Now&nbsp;<\/strong>button.<\/li>\n<\/ul><div class=\"wp-block-image\">\n<figure class=\"aligncenter size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"621\" height=\"580\" src=\"https:\/\/www.stellarinfo.com\/blog\/wp-content\/uploads\/2020\/08\/Outlook-data-file-seetings.png\" alt=\"Click on the Compact Now&nbsp;button\" class=\"wp-image-63466 apply-gradient-on-post-images\" srcset=\"https:\/\/www.stellarinfo.com\/blog\/wp-content\/uploads\/2020\/08\/Outlook-data-file-seetings.png 621w, https:\/\/www.stellarinfo.com\/blog\/wp-content\/uploads\/2020\/08\/Outlook-data-file-seetings-300x280.png 300w\" sizes=\"auto, (max-width: 621px) 100vw, 621px\" \/><\/figure>\n<\/div><ul class=\"wp-block-list\">\n<li>Then, click&nbsp;<strong>OK.<\/strong><\/li>\n<\/ul><p>This process will <strong>compact your OST<\/strong> file and reduce the size of your OST file.<\/p><blockquote class=\"note_alert\">\n<p><strong>Note<em>:<\/em><\/strong><em> Outlook automatically compacts the OST file in the background when unused white space exceeds 20% of the total file size. Manual compacting gives you immediate control over when this happens.<\/em><\/p>\n<\/blockquote><p><strong><em>Source: <\/em><\/strong><a href=\"https:\/\/support.microsoft.com\/en-us\/office\/reduce-the-size-of-your-mailbox-and-outlook-data-files-pst-and-ost-e4c6a4f1-d39c-47dc-a4fa-abe96dc8c7ef?utm_source=chatgpt.com\" target=\"_blank\" rel=\"noreferrer noopener nofollow\"><strong><em>Microsoft Docs &ndash; Reduce the size of an Outlook data file<\/em><\/strong><\/a><\/p><blockquote class=\"note_alert\">\n<p><em>&ldquo;Outlook&rsquo;s Compact Now feature is often misunderstood. It does not shrink the file by deleting data &mdash; it reclaims the empty space left behind after items are permanently removed. Think of it like compressing a half-empty box. The data hasn&rsquo;t changed, but the container is smaller. For best results, empty all deletion folders before compacting.&rdquo;<\/em><\/p>\n\n\n\n<p><strong>&mdash; Diane Poremsky, Microsoft Outlook MVP<\/strong> <em>Outlook Tips &amp; Slipstick Systems | outlook-tips.net<\/em><\/p>\n<\/blockquote><h3 class=\"wp-block-heading\"><strong>Method 2. Use &lsquo;Mailbox Cleanup&rsquo; Option in Outlook<\/strong><\/h3><p>Outlook&rsquo;s Mailbox Cleanup tool can help you manage the size of your OST file. It primarily helps you identify and delete unnecessary items to free up mailbox space. Here&rsquo;s how:<\/p><ul class=\"wp-block-list\">\n<li>Go to&nbsp;<strong>File &gt;&nbsp;Info.<\/strong>&nbsp;<\/li>\n\n\n\n<li>Click the <strong>Cleanup Tools<\/strong> dropdown button<\/li>\n\n\n\n<li>Then select <strong>Mailbox Cleanup<\/strong> from the menu<\/li>\n<\/ul><div class=\"wp-block-image\">\n<figure class=\"aligncenter size-large is-resized\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"520\" src=\"https:\/\/www.stellarinfo.com\/blog\/wp-content\/uploads\/2020\/08\/Outlook-account-information.png\" alt=\"select Mailbox Cleanup from the menu\" class=\"wp-image-63467 apply-gradient-on-post-images\" style=\"aspect-ratio:1.9692662734898714;width:780px;height:auto\" srcset=\"https:\/\/www.stellarinfo.com\/blog\/wp-content\/uploads\/2020\/08\/Outlook-account-information.png 1024w, https:\/\/www.stellarinfo.com\/blog\/wp-content\/uploads\/2020\/08\/Outlook-account-information-300x152.png 300w, https:\/\/www.stellarinfo.com\/blog\/wp-content\/uploads\/2020\/08\/Outlook-account-information-768x390.png 768w\" sizes=\"auto, (max-width: 1024px) 100vw, 1024px\" \/><\/figure>\n<\/div><div class=\"wp-block-image\">\n<figure class=\"aligncenter size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"776\" height=\"326\" src=\"https:\/\/www.stellarinfo.com\/blog\/wp-content\/uploads\/2020\/08\/Mailbox-cleanup.png\" alt=\"select Mailbox Cleanup \" class=\"wp-image-63468 apply-gradient-on-post-images\" srcset=\"https:\/\/www.stellarinfo.com\/blog\/wp-content\/uploads\/2020\/08\/Mailbox-cleanup.png 776w, https:\/\/www.stellarinfo.com\/blog\/wp-content\/uploads\/2020\/08\/Mailbox-cleanup-300x126.png 300w, https:\/\/www.stellarinfo.com\/blog\/wp-content\/uploads\/2020\/08\/Mailbox-cleanup-768x323.png 768w\" sizes=\"auto, (max-width: 776px) 100vw, 776px\" \/><\/figure>\n<\/div><ul class=\"wp-block-list\">\n<li>In&nbsp;<strong>Mailbox Cleanup<\/strong>&nbsp;dialog box, click on &lsquo;<strong>View Mailbox Size&hellip;<\/strong>&rsquo; button.<\/li>\n<\/ul><div class=\"wp-block-image\">\n<figure class=\"aligncenter size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"400\" height=\"345\" src=\"https:\/\/www.stellarinfo.com\/blog\/wp-content\/uploads\/2020\/08\/check-mailbox-size.png\" alt=\"click on View Mailbox Size\" class=\"wp-image-63470 apply-gradient-on-post-images\" srcset=\"https:\/\/www.stellarinfo.com\/blog\/wp-content\/uploads\/2020\/08\/check-mailbox-size.png 400w, https:\/\/www.stellarinfo.com\/blog\/wp-content\/uploads\/2020\/08\/check-mailbox-size-300x259.png 300w\" sizes=\"auto, (max-width: 400px) 100vw, 400px\" \/><\/figure>\n<\/div><ul class=\"wp-block-list\">\n<li>To compact OST file, choose any of the following options:\n<ul class=\"wp-block-list\">\n<li><strong>Find items older than:<\/strong>&nbsp;To find and delete emails older than a certain number of days that you don&rsquo;t require anymore.<\/li>\n\n\n\n<li><strong>Find items large than:&nbsp;<\/strong>To find and delete emails larger than a certain size.<\/li>\n<\/ul>\n<\/li>\n<\/ul><div class=\"wp-block-image\">\n<figure class=\"aligncenter size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"410\" height=\"362\" src=\"https:\/\/www.stellarinfo.com\/blog\/wp-content\/uploads\/2020\/08\/Mailbox-cleanup-options.png\" alt=\" View Mailbox Size\" class=\"wp-image-63469 apply-gradient-on-post-images\" srcset=\"https:\/\/www.stellarinfo.com\/blog\/wp-content\/uploads\/2020\/08\/Mailbox-cleanup-options.png 410w, https:\/\/www.stellarinfo.com\/blog\/wp-content\/uploads\/2020\/08\/Mailbox-cleanup-options-300x265.png 300w\" sizes=\"auto, (max-width: 410px) 100vw, 410px\" \/><\/figure>\n<\/div><ul class=\"wp-block-list\">\n<li>Alternatively, you can &lsquo;<em>Empty Deleted Items&nbsp;folder<\/em>,&rsquo; &lsquo;<em>View Deleted Items Size<\/em>,&rsquo;&nbsp;&lsquo;<em>View Conflicts Size<\/em>&rsquo;, or&nbsp;&lsquo;<em>Empty Conflicts<\/em>&rsquo;&nbsp;to compress the OST file.<\/li>\n<\/ul><p>After deleting items using Mailbox Cleanup, run <strong>Compact Now<\/strong> (see Method 1) to reclaim the resulting white space from the OST file. Mailbox Cleanup alone does not reduce the OST file size&mdash;the freed space only becomes available after compacting.<\/p><p>In case you want to compact OST without deleting older emails, follow the next method.<\/p><h3 class=\"wp-block-heading\"><strong>Method 3.&nbsp; Archive Old Emails to PST<\/strong><\/h3><p>This feature moves items OUT of the OST cache into a separate PST file on disk. You can use this method to keep older emails by exporting the emails to a local PST or personal folder file. This can help&nbsp;<a href=\"https:\/\/www.stellarinfo.com\/blog\/ost-file-reached-maximum-size\/\">reduce OST size<\/a>&nbsp;significantly without deleting a single email. Here&rsquo;s how:<\/p><ul class=\"wp-block-list\">\n<li>In Outlook 2013,\n<ul class=\"wp-block-list\">\n<li>Go to&nbsp;<strong>File &gt; Cleanup Tools &gt; Archive<\/strong>.&nbsp;<\/li>\n<\/ul>\n<\/li>\n<\/ul><div class=\"wp-block-image\">\n<figure class=\"aligncenter size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"322\" height=\"277\" src=\"https:\/\/www.stellarinfo.com\/blog\/wp-content\/uploads\/2020\/08\/Archive-mailbox.jpg\" alt=\"Go to&nbsp;File &gt; Cleanup Tools &gt; Archive\" class=\"wp-image-63471 apply-gradient-on-post-images\" srcset=\"https:\/\/www.stellarinfo.com\/blog\/wp-content\/uploads\/2020\/08\/Archive-mailbox.jpg 322w, https:\/\/www.stellarinfo.com\/blog\/wp-content\/uploads\/2020\/08\/Archive-mailbox-300x258.jpg 300w\" sizes=\"auto, (max-width: 322px) 100vw, 322px\" \/><\/figure>\n<\/div><ul class=\"wp-block-list\">\n<li>In Outlook 2016 or 2019,\n<ul class=\"wp-block-list\">\n<li>Navigate to&nbsp;<strong>File &gt; Info &gt; Tools &gt; Clean up old items.<\/strong><\/li>\n<\/ul>\n<\/li>\n<\/ul><div class=\"wp-block-image\">\n<figure class=\"aligncenter size-large is-resized\"><img loading=\"lazy\" decoding=\"async\" width=\"304\" height=\"341\" src=\"https:\/\/www.stellarinfo.com\/blog\/wp-content\/uploads\/2020\/08\/Clean-up-old-items.png\" alt=\"Nevigate to File &gt; Info &gt; Tools &gt; Clean up old items\" class=\"wp-image-63472 apply-gradient-on-post-images\" style=\"aspect-ratio:0.8915314819906517;width:304px;height:auto\" srcset=\"https:\/\/www.stellarinfo.com\/blog\/wp-content\/uploads\/2020\/08\/Clean-up-old-items.png 304w, https:\/\/www.stellarinfo.com\/blog\/wp-content\/uploads\/2020\/08\/Clean-up-old-items-267x300.png 267w\" sizes=\"auto, (max-width: 304px) 100vw, 304px\" \/><\/figure>\n<\/div><ul class=\"wp-block-list\">\n<li>Select the&nbsp;&lsquo;<strong>Archive this folder and all subfolders&rsquo;<\/strong>&nbsp;option.<\/li>\n\n\n\n<li>Choose an email folder from the list for the&nbsp;<strong>Archive.<\/strong><\/li>\n\n\n\n<li>Then, choose the date in the &lsquo;<strong>Archive items older than:<\/strong>&rsquo; option.<\/li>\n<\/ul><div class=\"wp-block-image\">\n<figure class=\"aligncenter size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"328\" height=\"351\" src=\"https:\/\/www.stellarinfo.com\/blog\/wp-content\/uploads\/2020\/08\/Archive-older-items-via-date.jpg\" alt=\"Archive items older than\" class=\"wp-image-63473 apply-gradient-on-post-images\" srcset=\"https:\/\/www.stellarinfo.com\/blog\/wp-content\/uploads\/2020\/08\/Archive-older-items-via-date.jpg 328w, https:\/\/www.stellarinfo.com\/blog\/wp-content\/uploads\/2020\/08\/Archive-older-items-via-date-280x300.jpg 280w\" sizes=\"auto, (max-width: 328px) 100vw, 328px\" \/><\/figure>\n<\/div><ul class=\"wp-block-list\">\n<li>Click on&nbsp;<strong>Browse&nbsp;<\/strong>to select a save location.<\/li>\n\n\n\n<li>Then click&nbsp;<strong>OK.<\/strong><\/li>\n<\/ul><p>You can also set Up AutoArchive for automatic cleanup. To automate this process and prevent the OST file from growing too large again, you can enable AutoArchive:<\/p><ul class=\"wp-block-list\">\n<li>Go to <strong>File &gt; Options &gt; Advanced<\/strong><\/li>\n<\/ul><figure class=\"wp-block-image size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"818\" height=\"672\" src=\"https:\/\/www.stellarinfo.com\/blog\/wp-content\/uploads\/2020\/08\/Outlook-options.png\" alt=\"Go to File &gt; Options &gt; Advanced\" class=\"wp-image-191570 apply-gradient-on-post-images\" srcset=\"https:\/\/www.stellarinfo.com\/blog\/wp-content\/uploads\/2020\/08\/Outlook-options.png 818w, https:\/\/www.stellarinfo.com\/blog\/wp-content\/uploads\/2020\/08\/Outlook-options-300x246.png 300w, https:\/\/www.stellarinfo.com\/blog\/wp-content\/uploads\/2020\/08\/Outlook-options-768x631.png 768w\" sizes=\"auto, (max-width: 818px) 100vw, 818px\" \/><\/figure><ul class=\"wp-block-list\">\n<li>Under the <strong>AutoArchive<\/strong> section, click <strong>AutoArchive<\/strong> Settings<\/li>\n\n\n\n<li>Check Run AutoArchive every [X] days<\/li>\n\n\n\n<li>Configure the preferred archive settings such as folder cleanup frequency, old item removal, and archive file location<\/li>\n\n\n\n<li>Click <strong>OK<\/strong> to save the settings<\/li>\n<\/ul><p>This helps Outlook automatically move older emails to a PST file at regular intervals.<\/p><blockquote class=\"note_alert\">\n<p><strong>Note:<\/strong> <em>After archiving completes, run Compact Now (see Method 1) to reclaim the white space left in the OST file by the moved items. Refer <\/em><a href=\"https:\/\/learn.microsoft.com\/en-US\/outlook\/troubleshoot\/data-files\/how-to-manage-pst-files\" target=\"_blank\" rel=\"noreferrer noopener nofollow\">Microsoft&rsquo;s official documentation on managing PST files<\/a> for detailed guidance.<\/p>\n<\/blockquote><h3 class=\"wp-block-heading\"><strong>4. Convert the OST File to PST<\/strong><\/h3><p>If the methods mentioned above fail to compact the OST file or your data file is corrupted, then converting it to PST format is the most reliable option. You can convert your OST file to PST format by using <a href=\"https:\/\/www.stellarinfo.com\/convert-ost-to-pst.php\"><strong>Stellar Converter for OST <\/strong><\/a>&nbsp;&ndash; an advanced OST to PST converter tool. This tool converts your large-sized OST file to PST and provides two options:<\/p><ul class=\"wp-block-list\">\n<li><strong>Compact and Save PST: <\/strong>This option allows you to extract email attachments and save them in a separate folder, while preserving the attachment links with their respective emails. This reduces the PST file size to a few MBs or GBs. Now you will be able to access the PST file in Outlook and all the attached links. The Technician version of this tool includes this option.<\/li>\n\n\n\n<li><strong>Split and Save PST:<\/strong> You can use this option to split resultant PST file on the basis of mail ids, date, size. This feature helps you to split large PST file and keep the original hierarchy of the mailbox.&nbsp;<\/li>\n<\/ul><p>Additionally, Stellar Converter for OST &ndash; Technician offers features such as:<\/p><ul class=\"wp-block-list\">\n<li>Converts OST file to PST with 100% accuracy.<\/li>\n\n\n\n<li>Allows saving converted data in multiple file formats including PDF, HTML, RTF, EML, and MSG.<\/li>\n\n\n\n<li>Option to directly export OST data to live Exchange Server.<\/li>\n\n\n\n<li>Supports migration of OST data to Office 365.<\/li>\n\n\n\n<li>Allows exporting mailbox data to an existing Outlook profile.<\/li>\n\n\n\n<li>Maintains original folder structure and data integrity during conversion.<\/li>\n\n\n\n<li>Supports conversion of large and inaccessible OST files.<\/li>\n\n\n\n<li>Provides preview of mailbox items before saving. &nbsp;<\/li>\n<\/ul><h2 class=\"wp-block-heading\" id=\"which-method-you-should-choose-to-compact-ost-file?\"><strong>Which Method you should Choose to Compact OST File?<\/strong><\/h2><p>You can choose the method that is suitable for your specific needs. Below are the key differences:<\/p><figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><tbody><tr><td><strong>Method<\/strong><\/td><td><strong>Purpose<\/strong><\/td><td><strong>What It Does<\/strong><\/td><td><strong>Deletes Emails<\/strong><\/td><td><strong>Risk Level<\/strong><\/td><td><strong>Best For<\/strong><\/td><td><strong>Difficulty Level<\/strong><\/td><\/tr><tr><td><strong>Compact Now<\/strong><\/td><td>Reduce OST size<\/td><td>Removes white space left after deleted items<\/td><td>No<\/td><td>Very Low<\/td><td>Quick and safe size reduction<\/td><td>Easy<\/td><\/tr><tr><td><strong>Mailbox Cleanup<\/strong><\/td><td>Free up mailbox space<\/td><td>Finds and deletes old or large emails<\/td><td>Yes (Selective)<\/td><td>Moderate<\/td><td>Ongoing mailbox maintenance<\/td><td>Easy<\/td><\/tr><tr><td><strong>Archive Old Emails<\/strong><\/td><td>Move older emails<\/td><td>Moves emails from OST to PST file<\/td><td>No (Moves data)<\/td><td>Low<\/td><td>Keeping all emails while reducing OST size<\/td><td>Moderate<\/td><\/tr><tr><td><strong>OST Converter<\/strong><\/td><td>Recover &amp; rebuild mailbox<\/td><td>Converts OST to new PST file<\/td><td>No<\/td><td>Very Low<\/td><td>Recovering Mail Items from Large, Corrupt, inaccessible, or orphaned OST Files<\/td><td>Easy (DIY Tool)<\/td><\/tr><\/tbody><\/table><\/figure><h2 class=\"wp-block-heading\" id=\"conclusion\"><strong>Conclusion<\/strong><\/h2><p>A large OST file can cause issues and errors in Outlook. You can prevent these problems and errors by compacting the OST file. Above, we have explained various ways by which OST files are compacted using built-in MS Outlook features. If these features are unable to compact the OST file, then advanced OST to PST converter software such as Stellar converter for OST is the only option. This converter converts the inaccessible OST to PST and splits the converted PST file into multiple files. It also provides an advanced option to save attachments in a separate folder that helps compact the resultant PST file.<\/p><h2 class=\"wp-block-heading\" id=\"faqs\">FAQs<\/h2><p><\/p>\n","protected":false},"excerpt":{"rendered":"<p>In Outlook, to compact the OST file, open the Account Settings &gt;&hellip; <a class=\"more-link\" href=\"https:\/\/www.stellarinfo.com\/blog\/compact-outlook-ost-file\/\">Continue reading <span class=\"screen-reader-text\">How to Compact OST File in Outlook?<\/span><\/a><\/p>\n","protected":false},"author":105,"featured_media":63633,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[821],"tags":[3274],"class_list":["post-63462","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-outlook-data-file","tag-compact-ost-file","entry"],"acf":[],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v26.9 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\n<title>How to Compact OST File in Outlook?<\/title>\n<meta name=\"description\" content=\"Learn how to compact Outlook OST file using Compact Now, Mailbox Cleanup, Archiving, and OST-to-PST conversion. Step-by-step guide for all Outlook versions\" \/>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/www.stellarinfo.com\/blog\/compact-outlook-ost-file\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"How to Compact OST File in Outlook?\" \/>\n<meta property=\"og:description\" content=\"Learn how to compact Outlook OST file using Compact Now, Mailbox Cleanup, Archiving, and OST-to-PST conversion. Step-by-step guide for all Outlook versions\" \/>\n<meta property=\"og:url\" content=\"https:\/\/www.stellarinfo.com\/blog\/compact-outlook-ost-file\/\" \/>\n<meta property=\"og:site_name\" content=\"Stellar Data Recovery Blog\" \/>\n<meta property=\"article:published_time\" content=\"2020-08-27T11:41:29+00:00\" \/>\n<meta property=\"article:modified_time\" content=\"2026-05-07T05:35:37+00:00\" \/>\n<meta property=\"og:image\" content=\"https:\/\/www.stellarinfo.com\/blog\/wp-content\/uploads\/2020\/08\/How-to-Compact-OST-File.jpg\" \/>\n\t<meta property=\"og:image:width\" content=\"1000\" \/>\n\t<meta property=\"og:image:height\" content=\"600\" \/>\n\t<meta property=\"og:image:type\" content=\"image\/jpeg\" \/>\n<meta name=\"author\" content=\"Jyoti Singh\" \/>\n<meta name=\"twitter:card\" content=\"summary_large_image\" \/>\n<meta name=\"twitter:label1\" content=\"Written by\" \/>\n\t<meta name=\"twitter:data1\" content=\"Jyoti Singh\" \/>\n\t<meta name=\"twitter:label2\" content=\"Est. reading time\" \/>\n\t<meta name=\"twitter:data2\" content=\"10 minutes\" \/>\n<script type=\"application\/ld+json\" class=\"yoast-schema-graph\">{\"@context\":\"https:\/\/schema.org\",\"@graph\":[{\"@type\":\"Article\",\"@id\":\"https:\/\/www.stellarinfo.com\/blog\/compact-outlook-ost-file\/#article\",\"isPartOf\":{\"@id\":\"https:\/\/www.stellarinfo.com\/blog\/compact-outlook-ost-file\/\"},\"author\":{\"name\":\"Jyoti Singh\",\"@id\":\"https:\/\/www.stellarinfo.com\/blog\/#\/schema\/person\/2778f102d97c6f22d0884b5ba569379f\"},\"headline\":\"How to Compact OST File in Outlook?\",\"datePublished\":\"2020-08-27T11:41:29+00:00\",\"dateModified\":\"2026-05-07T05:35:37+00:00\",\"mainEntityOfPage\":{\"@id\":\"https:\/\/www.stellarinfo.com\/blog\/compact-outlook-ost-file\/\"},\"wordCount\":1737,\"commentCount\":0,\"image\":{\"@id\":\"https:\/\/www.stellarinfo.com\/blog\/compact-outlook-ost-file\/#primaryimage\"},\"thumbnailUrl\":\"https:\/\/www.stellarinfo.com\/blog\/wp-content\/uploads\/2020\/08\/How-to-Compact-OST-File.jpg\",\"keywords\":[\"Compact OST file\"],\"articleSection\":[\"OST to PST Converter\"],\"inLanguage\":\"en-US\",\"potentialAction\":[{\"@type\":\"CommentAction\",\"name\":\"Comment\",\"target\":[\"https:\/\/www.stellarinfo.com\/blog\/compact-outlook-ost-file\/#respond\"]}]},{\"@type\":\"WebPage\",\"@id\":\"https:\/\/www.stellarinfo.com\/blog\/compact-outlook-ost-file\/\",\"url\":\"https:\/\/www.stellarinfo.com\/blog\/compact-outlook-ost-file\/\",\"name\":\"How to Compact OST File in Outlook?\",\"isPartOf\":{\"@id\":\"https:\/\/www.stellarinfo.com\/blog\/#website\"},\"primaryImageOfPage\":{\"@id\":\"https:\/\/www.stellarinfo.com\/blog\/compact-outlook-ost-file\/#primaryimage\"},\"image\":{\"@id\":\"https:\/\/www.stellarinfo.com\/blog\/compact-outlook-ost-file\/#primaryimage\"},\"thumbnailUrl\":\"https:\/\/www.stellarinfo.com\/blog\/wp-content\/uploads\/2020\/08\/How-to-Compact-OST-File.jpg\",\"datePublished\":\"2020-08-27T11:41:29+00:00\",\"dateModified\":\"2026-05-07T05:35:37+00:00\",\"author\":{\"@id\":\"https:\/\/www.stellarinfo.com\/blog\/#\/schema\/person\/2778f102d97c6f22d0884b5ba569379f\"},\"description\":\"Learn how to compact Outlook OST file using Compact Now, Mailbox Cleanup, Archiving, and OST-to-PST conversion. Step-by-step guide for all Outlook versions\",\"breadcrumb\":{\"@id\":\"https:\/\/www.stellarinfo.com\/blog\/compact-outlook-ost-file\/#breadcrumb\"},\"inLanguage\":\"en-US\",\"potentialAction\":[{\"@type\":\"ReadAction\",\"target\":[\"https:\/\/www.stellarinfo.com\/blog\/compact-outlook-ost-file\/\"]}]},{\"@type\":\"ImageObject\",\"inLanguage\":\"en-US\",\"@id\":\"https:\/\/www.stellarinfo.com\/blog\/compact-outlook-ost-file\/#primaryimage\",\"url\":\"https:\/\/www.stellarinfo.com\/blog\/wp-content\/uploads\/2020\/08\/How-to-Compact-OST-File.jpg\",\"contentUrl\":\"https:\/\/www.stellarinfo.com\/blog\/wp-content\/uploads\/2020\/08\/How-to-Compact-OST-File.jpg\",\"width\":1000,\"height\":600,\"caption\":\"How to Compact OST File?\"},{\"@type\":\"BreadcrumbList\",\"@id\":\"https:\/\/www.stellarinfo.com\/blog\/compact-outlook-ost-file\/#breadcrumb\",\"itemListElement\":[{\"@type\":\"ListItem\",\"position\":1,\"name\":\"Home\",\"item\":\"https:\/\/www.stellarinfo.com\/blog\/\"},{\"@type\":\"ListItem\",\"position\":2,\"name\":\"How to Compact OST File in Outlook?\"}]},{\"@type\":\"WebSite\",\"@id\":\"https:\/\/www.stellarinfo.com\/blog\/#website\",\"url\":\"https:\/\/www.stellarinfo.com\/blog\/\",\"name\":\"Stellar Data Recovery Blog\",\"description\":\"\",\"potentialAction\":[{\"@type\":\"SearchAction\",\"target\":{\"@type\":\"EntryPoint\",\"urlTemplate\":\"https:\/\/www.stellarinfo.com\/blog\/?s={search_term_string}\"},\"query-input\":{\"@type\":\"PropertyValueSpecification\",\"valueRequired\":true,\"valueName\":\"search_term_string\"}}],\"inLanguage\":\"en-US\"},{\"@type\":\"Person\",\"@id\":\"https:\/\/www.stellarinfo.com\/blog\/#\/schema\/person\/2778f102d97c6f22d0884b5ba569379f\",\"name\":\"Jyoti Singh\",\"image\":{\"@type\":\"ImageObject\",\"inLanguage\":\"en-US\",\"@id\":\"https:\/\/www.stellarinfo.com\/blog\/#\/schema\/person\/image\/\",\"url\":\"https:\/\/secure.gravatar.com\/avatar\/2f174fb1c0f9d564efe9ae999e8f57dd20c7369fb7fb3ae948d63d2d5cc09d1b?s=96&d=mm&r=g\",\"contentUrl\":\"https:\/\/secure.gravatar.com\/avatar\/2f174fb1c0f9d564efe9ae999e8f57dd20c7369fb7fb3ae948d63d2d5cc09d1b?s=96&d=mm&r=g\",\"caption\":\"Jyoti Singh\"},\"description\":\"Jyoti is a Senior Content Writer at Stellar, specializes in simplifying complex concepts in an easy-to-understand way for the end users. Her core expertise lies in providing solutions related to MS Outlook, Microsoft 365 and other email platforms. She focuses on addressing real-world challenges, such as data file (mailbox) corruption and data accessibility issues, helping the users find practical and reliable solutions.\",\"url\":\"https:\/\/www.stellarinfo.com\/blog\/author\/jyotisingh\/\"}]}<\/script>\n<!-- \/ Yoast SEO plugin. -->","yoast_head_json":{"title":"How to Compact OST File in Outlook?","description":"Learn how to compact Outlook OST file using Compact Now, Mailbox Cleanup, Archiving, and OST-to-PST conversion. Step-by-step guide for all Outlook versions","robots":{"index":"index","follow":"follow","max-snippet":"max-snippet:-1","max-image-preview":"max-image-preview:large","max-video-preview":"max-video-preview:-1"},"canonical":"https:\/\/www.stellarinfo.com\/blog\/compact-outlook-ost-file\/","og_locale":"en_US","og_type":"article","og_title":"How to Compact OST File in Outlook?","og_description":"Learn how to compact Outlook OST file using Compact Now, Mailbox Cleanup, Archiving, and OST-to-PST conversion. Step-by-step guide for all Outlook versions","og_url":"https:\/\/www.stellarinfo.com\/blog\/compact-outlook-ost-file\/","og_site_name":"Stellar Data Recovery Blog","article_published_time":"2020-08-27T11:41:29+00:00","article_modified_time":"2026-05-07T05:35:37+00:00","og_image":[{"width":1000,"height":600,"url":"https:\/\/www.stellarinfo.com\/blog\/wp-content\/uploads\/2020\/08\/How-to-Compact-OST-File.jpg","type":"image\/jpeg"}],"author":"Jyoti Singh","twitter_card":"summary_large_image","twitter_misc":{"Written by":"Jyoti Singh","Est. reading time":"10 minutes"},"schema":{"@context":"https:\/\/schema.org","@graph":[{"@type":"Article","@id":"https:\/\/www.stellarinfo.com\/blog\/compact-outlook-ost-file\/#article","isPartOf":{"@id":"https:\/\/www.stellarinfo.com\/blog\/compact-outlook-ost-file\/"},"author":{"name":"Jyoti Singh","@id":"https:\/\/www.stellarinfo.com\/blog\/#\/schema\/person\/2778f102d97c6f22d0884b5ba569379f"},"headline":"How to Compact OST File in Outlook?","datePublished":"2020-08-27T11:41:29+00:00","dateModified":"2026-05-07T05:35:37+00:00","mainEntityOfPage":{"@id":"https:\/\/www.stellarinfo.com\/blog\/compact-outlook-ost-file\/"},"wordCount":1737,"commentCount":0,"image":{"@id":"https:\/\/www.stellarinfo.com\/blog\/compact-outlook-ost-file\/#primaryimage"},"thumbnailUrl":"https:\/\/www.stellarinfo.com\/blog\/wp-content\/uploads\/2020\/08\/How-to-Compact-OST-File.jpg","keywords":["Compact OST file"],"articleSection":["OST to PST Converter"],"inLanguage":"en-US","potentialAction":[{"@type":"CommentAction","name":"Comment","target":["https:\/\/www.stellarinfo.com\/blog\/compact-outlook-ost-file\/#respond"]}]},{"@type":"WebPage","@id":"https:\/\/www.stellarinfo.com\/blog\/compact-outlook-ost-file\/","url":"https:\/\/www.stellarinfo.com\/blog\/compact-outlook-ost-file\/","name":"How to Compact OST File in Outlook?","isPartOf":{"@id":"https:\/\/www.stellarinfo.com\/blog\/#website"},"primaryImageOfPage":{"@id":"https:\/\/www.stellarinfo.com\/blog\/compact-outlook-ost-file\/#primaryimage"},"image":{"@id":"https:\/\/www.stellarinfo.com\/blog\/compact-outlook-ost-file\/#primaryimage"},"thumbnailUrl":"https:\/\/www.stellarinfo.com\/blog\/wp-content\/uploads\/2020\/08\/How-to-Compact-OST-File.jpg","datePublished":"2020-08-27T11:41:29+00:00","dateModified":"2026-05-07T05:35:37+00:00","author":{"@id":"https:\/\/www.stellarinfo.com\/blog\/#\/schema\/person\/2778f102d97c6f22d0884b5ba569379f"},"description":"Learn how to compact Outlook OST file using Compact Now, Mailbox Cleanup, Archiving, and OST-to-PST conversion. Step-by-step guide for all Outlook versions","breadcrumb":{"@id":"https:\/\/www.stellarinfo.com\/blog\/compact-outlook-ost-file\/#breadcrumb"},"inLanguage":"en-US","potentialAction":[{"@type":"ReadAction","target":["https:\/\/www.stellarinfo.com\/blog\/compact-outlook-ost-file\/"]}]},{"@type":"ImageObject","inLanguage":"en-US","@id":"https:\/\/www.stellarinfo.com\/blog\/compact-outlook-ost-file\/#primaryimage","url":"https:\/\/www.stellarinfo.com\/blog\/wp-content\/uploads\/2020\/08\/How-to-Compact-OST-File.jpg","contentUrl":"https:\/\/www.stellarinfo.com\/blog\/wp-content\/uploads\/2020\/08\/How-to-Compact-OST-File.jpg","width":1000,"height":600,"caption":"How to Compact OST File?"},{"@type":"BreadcrumbList","@id":"https:\/\/www.stellarinfo.com\/blog\/compact-outlook-ost-file\/#breadcrumb","itemListElement":[{"@type":"ListItem","position":1,"name":"Home","item":"https:\/\/www.stellarinfo.com\/blog\/"},{"@type":"ListItem","position":2,"name":"How to Compact OST File in Outlook?"}]},{"@type":"WebSite","@id":"https:\/\/www.stellarinfo.com\/blog\/#website","url":"https:\/\/www.stellarinfo.com\/blog\/","name":"Stellar Data Recovery Blog","description":"","potentialAction":[{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https:\/\/www.stellarinfo.com\/blog\/?s={search_term_string}"},"query-input":{"@type":"PropertyValueSpecification","valueRequired":true,"valueName":"search_term_string"}}],"inLanguage":"en-US"},{"@type":"Person","@id":"https:\/\/www.stellarinfo.com\/blog\/#\/schema\/person\/2778f102d97c6f22d0884b5ba569379f","name":"Jyoti Singh","image":{"@type":"ImageObject","inLanguage":"en-US","@id":"https:\/\/www.stellarinfo.com\/blog\/#\/schema\/person\/image\/","url":"https:\/\/secure.gravatar.com\/avatar\/2f174fb1c0f9d564efe9ae999e8f57dd20c7369fb7fb3ae948d63d2d5cc09d1b?s=96&d=mm&r=g","contentUrl":"https:\/\/secure.gravatar.com\/avatar\/2f174fb1c0f9d564efe9ae999e8f57dd20c7369fb7fb3ae948d63d2d5cc09d1b?s=96&d=mm&r=g","caption":"Jyoti Singh"},"description":"Jyoti is a Senior Content Writer at Stellar, specializes in simplifying complex concepts in an easy-to-understand way for the end users. Her core expertise lies in providing solutions related to MS Outlook, Microsoft 365 and other email platforms. She focuses on addressing real-world challenges, such as data file (mailbox) corruption and data accessibility issues, helping the users find practical and reliable solutions.","url":"https:\/\/www.stellarinfo.com\/blog\/author\/jyotisingh\/"}]}},"_links":{"self":[{"href":"https:\/\/www.stellarinfo.com\/blog\/wp-json\/wp\/v2\/posts\/63462","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.stellarinfo.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.stellarinfo.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.stellarinfo.com\/blog\/wp-json\/wp\/v2\/users\/105"}],"replies":[{"embeddable":true,"href":"https:\/\/www.stellarinfo.com\/blog\/wp-json\/wp\/v2\/comments?post=63462"}],"version-history":[{"count":16,"href":"https:\/\/www.stellarinfo.com\/blog\/wp-json\/wp\/v2\/posts\/63462\/revisions"}],"predecessor-version":[{"id":191709,"href":"https:\/\/www.stellarinfo.com\/blog\/wp-json\/wp\/v2\/posts\/63462\/revisions\/191709"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.stellarinfo.com\/blog\/wp-json\/wp\/v2\/media\/63633"}],"wp:attachment":[{"href":"https:\/\/www.stellarinfo.com\/blog\/wp-json\/wp\/v2\/media?parent=63462"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.stellarinfo.com\/blog\/wp-json\/wp\/v2\/categories?post=63462"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.stellarinfo.com\/blog\/wp-json\/wp\/v2\/tags?post=63462"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}