{"id":2323,"date":"2026-03-24T20:32:30","date_gmt":"2026-03-24T15:02:30","guid":{"rendered":"https:\/\/mukundasoftware.com\/blog\/?p=2323"},"modified":"2026-03-24T20:33:05","modified_gmt":"2026-03-24T15:03:05","slug":"fix-msoutlook-runs-slowly-or-crashes-oversized-pst-file-performance","status":"publish","type":"post","link":"https:\/\/mukundasoftware.com\/blog\/help\/outlook\/fix-msoutlook-runs-slowly-or-crashes-oversized-pst-file-performance.html","title":{"rendered":"Fix: MS Outlook Runs Slowly or Crashes \u2013 Oversized PST File Performance"},"content":{"rendered":"\n<blockquote class=\"wp-block-quote is-layout-flow wp-block-quote-is-layout-flow\">\n<p class=\"wp-block-paragraph\"><strong>TL;DR:<\/strong> Outlook performance degrades sharply when your PST file exceeds 20GB. The solution is to compact, split, or archive your data. Jump to Solution 3 to learn how to split your PST file safely.<\/p>\n<\/blockquote>\n\n\n\n<p class=\"wp-block-paragraph\">Few things test your patience like a sluggish Outlook\u2014endless \u201cNot Responding\u201d messages, delayed send\/receive, and random crashes. If your Outlook has become painfully slow, the most likely culprit is an <strong>oversized PST file<\/strong>.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Microsoft sets a <strong>recommended limit of 20GB<\/strong> for PST files. When you cross that threshold, performance drops dramatically. At 50GB (the hard limit for Outlook 2013 and later), corruption and crashes become common.<\/p>\n\n\n\n<blockquote class=\"wp-block-quote is-layout-flow wp-block-quote-is-layout-flow\">\n<p class=\"wp-block-paragraph\"><strong>\ud83d\udccc Important \u2013 SSD vs. HDD:<\/strong> Your storage drive plays a huge role. A 20GB PST on a modern <strong>Solid\u2011State Drive (SSD)<\/strong> may still perform acceptably. On a traditional <strong>Hard Disk Drive (HDD)<\/strong> , that same file can cause severe slowdowns, freezing, and long startup times. If your PST is large and you\u2019re using an HDD, upgrading to an SSD or reducing PST size becomes critical.<\/p>\n<\/blockquote>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\"><strong>What Causes Outlook to Slow Down?<\/strong><\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Outlook stores your email, calendar, contacts, and attachments in a <strong>Personal Storage Table (PST)<\/strong> file. Over time, this file grows as you accumulate emails. Common causes of performance issues include:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>PST file size exceeding 20GB<\/strong> \u2013 The primary performance threshold.<\/li>\n\n\n\n<li><strong>Fragmented PST file<\/strong> \u2013 Deleted items leave empty space, causing inefficient access.<\/li>\n\n\n\n<li><strong>AutoArchive disabled<\/strong> \u2013 Old emails never move out of the main PST.<\/li>\n\n\n\n<li><strong>Large attachments stored within the PST<\/strong> \u2013 Attachments bloat the file.<\/li>\n\n\n\n<li><strong>Corrupted PST file structure<\/strong> \u2013 Errors accumulate over time.<\/li>\n\n\n\n<li><strong>Add\u2011ins conflicting<\/strong> \u2013 Not directly PST\u2011related, but can compound slowdowns.<\/li>\n<\/ul>\n\n\n\n<blockquote class=\"wp-block-quote is-layout-flow wp-block-quote-is-layout-flow\">\n<p class=\"wp-block-paragraph\"><strong>\ud83d\udca1 Note on OST Files:<\/strong> If you use an <strong>Exchange<\/strong>, <strong>Microsoft 365<\/strong>, or <strong><a href=\"https:\/\/Outlook.com\" target=\"_blank\" rel=\"noreferrer noopener nofollow\">Outlook.com<\/a><\/strong> account, you may see an <strong>.OST<\/strong> (Offline Storage Table) file instead of a PST. The same performance rules apply\u2014<strong>keep OST files under 20GB<\/strong> for optimal speed. The steps for compacting, archiving, and splitting are nearly identical.<\/p>\n<\/blockquote>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\"><strong>How to Fix Outlook Slow Performance Due to Oversized PST<\/strong><\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Work through these solutions in order. Always back up your PST file before performing major operations.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h3 class=\"wp-block-heading\">1. Locate and Check Your PST File Size<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">First, confirm that a large PST is indeed the issue.<\/p>\n\n\n\n<ol start=\"1\" class=\"wp-block-list\">\n<li>In Outlook, go to <strong>File<\/strong> \u2192 <strong>Account Settings<\/strong> \u2192 <strong>Account Settings<\/strong>.<\/li>\n\n\n\n<li>Click the <strong>Data Files<\/strong> tab.<\/li>\n\n\n\n<li>You\u2019ll see a list of data files. The <strong>Name<\/strong> column often includes \u201cOutlook Data File\u201d or your email address. Look at the <strong>Size<\/strong> column.\n<ul class=\"wp-block-list\">\n<li>If any PST exceeds <strong>20GB<\/strong>, performance will be degraded.<\/li>\n\n\n\n<li>At <strong>50GB<\/strong> (or even earlier), corruption is likely.<\/li>\n<\/ul>\n<\/li>\n<\/ol>\n\n\n\n<blockquote class=\"wp-block-quote is-layout-flow wp-block-quote-is-layout-flow\">\n<p class=\"wp-block-paragraph\"><strong>Note:<\/strong> Outlook 2013 and later use a Unicode PST format with a theoretical limit of 50GB, but performance begins to suffer long before that. Microsoft officially recommends <strong>keeping PST files under 20GB<\/strong> for optimal performance.<\/p>\n<\/blockquote>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h3 class=\"wp-block-heading\">2. Compact the PST File<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">When you delete items, the PST file does not automatically shrink\u2014it retains empty space. Compacting reclaims that space.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Before compacting:<\/strong> Empty your <strong>Deleted Items<\/strong> folder and manually remove large emails with attachments.<\/p>\n\n\n\n<ol start=\"1\" class=\"wp-block-list\">\n<li>Close Outlook.<\/li>\n\n\n\n<li>Open <strong>Control Panel<\/strong> \u2192 <strong>Mail (Microsoft Outlook)<\/strong> \u2192 <strong>Data Files<\/strong>.<\/li>\n\n\n\n<li>Select your PST file and click <strong>Settings<\/strong>.<\/li>\n\n\n\n<li>Click <strong>Compact Now<\/strong>. This process may take several minutes to hours depending on file size.<\/li>\n\n\n\n<li>After completion, reopen Outlook and check performance.<\/li>\n<\/ol>\n\n\n\n<blockquote class=\"wp-block-quote is-layout-flow wp-block-quote-is-layout-flow\">\n<p class=\"wp-block-paragraph\"><strong>\u26a0\ufe0f The \u201cDelete + Compact\u201d Trap:<\/strong> Simply deleting 10GB of email <strong>does not shrink the PST file<\/strong> on your disk until you run <strong>Compact Now<\/strong>. Many users delete large amounts of data, see no change in disk space, and assume the deletion failed. Always follow deletions with a compact operation to reclaim space.<\/p>\n<\/blockquote>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h3 class=\"wp-block-heading\">3. Split the PST File into Smaller Parts<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">If your PST is well over 20GB, splitting it into multiple smaller PSTs is the most effective solution.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Method A \u2013 Create a New PST and Move Items:<\/strong><\/p>\n\n\n\n<ol start=\"1\" class=\"wp-block-list\">\n<li>Go to <strong>File<\/strong> \u2192 <strong>New Items<\/strong> \u2192 <strong>More Items<\/strong> \u2192 <strong>Outlook Data File<\/strong>.<\/li>\n\n\n\n<li>Give it a name (e.g., \u201cArchive 2024\u201d) and choose a save location.<\/li>\n\n\n\n<li>In the navigation pane, right\u2011click on folders you want to move (e.g., Sent Items from 2023) and select <strong>Move<\/strong> \u2192 <strong>Copy to Folder<\/strong> \u2192 choose the new PST.<\/li>\n\n\n\n<li>Repeat for large folders (Inbox subfolders, large Sent Items, etc.).<\/li>\n<\/ol>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Method B \u2013 Use Archive Feature (Manual):<\/strong><\/p>\n\n\n\n<ol start=\"1\" class=\"wp-block-list\">\n<li>Select the folders you want to archive.<\/li>\n\n\n\n<li>Go to <strong>File<\/strong> \u2192 <strong>Tools<\/strong> \u2192 <strong>Clean Up Old Items<\/strong>.<\/li>\n\n\n\n<li>Set a date to archive items older than, say, 2 years.<\/li>\n\n\n\n<li>Choose an archive file (or create a new PST) and run the archive.<\/li>\n<\/ol>\n\n\n\n<blockquote class=\"wp-block-quote is-layout-flow wp-block-quote-is-layout-flow\">\n<p class=\"wp-block-paragraph\"><strong>\u26a0\ufe0f Important:<\/strong> After moving items, the original PST may not shrink automatically. Run <strong>Compact Now<\/strong> (from step 2) to reclaim space.<\/p>\n<\/blockquote>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h3 class=\"wp-block-heading\">4. Enable AutoArchive to Prevent Future Bloat<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">AutoArchive automatically moves old items to a separate PST file, keeping your main PST lean.<\/p>\n\n\n\n<ol start=\"1\" class=\"wp-block-list\">\n<li>Go to <strong>File<\/strong> \u2192 <strong>Options<\/strong> \u2192 <strong>Advanced<\/strong>.<\/li>\n\n\n\n<li>Under <strong>AutoArchive<\/strong>, click <strong>AutoArchive Settings<\/strong>.<\/li>\n\n\n\n<li>Check <strong>Run AutoArchive every<\/strong> and set a frequency (e.g., 14 days).<\/li>\n\n\n\n<li>Choose <strong>Move old items to<\/strong> and select a destination PST file (or create one).<\/li>\n\n\n\n<li>Set folder\u2011specific policies by right\u2011clicking folders \u2192 <strong>Properties<\/strong> \u2192 <strong>AutoArchive<\/strong>.<\/li>\n<\/ol>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h3 class=\"wp-block-heading\">5. Remove Large Attachments<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">Attachments are the biggest space hogs. You can save attachments to your hard drive and remove them from emails.<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Use the <strong>Advanced Find<\/strong> feature:<br><strong>Search<\/strong> \u2192 <strong>Advanced Find<\/strong> \u2192 <strong>Advanced<\/strong> tab \u2192 <strong>Field<\/strong> \u2192 <strong>All Mail fields<\/strong> \u2192 <strong>Size<\/strong> \u2192 set a condition (e.g., \u201cgreater than\u201d 5,000 KB).<\/li>\n\n\n\n<li>Delete or save and remove attachments from large emails.<\/li>\n<\/ul>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h3 class=\"wp-block-heading\">6. Use the SCANPST Tool to Repair Corruption<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">If Outlook is already crashing, the PST file may be corrupted. Microsoft includes the <strong>Inbox Repair Tool<\/strong> (SCANPST.EXE) to fix errors.<\/p>\n\n\n\n<ol start=\"1\" class=\"wp-block-list\">\n<li>Close Outlook.<\/li>\n\n\n\n<li>Search your computer for <code>SCANPST.EXE<\/code> (typically in <code>C:\\Program Files\\Microsoft Office\\root\\OfficeXX\\<\/code>).<\/li>\n\n\n\n<li>Run it, browse to your PST file, and click <strong>Start<\/strong>.<\/li>\n\n\n\n<li>If errors are found, check <strong>Make backup before repairing<\/strong> and click <strong>Repair<\/strong>.<\/li>\n<\/ol>\n\n\n\n<blockquote class=\"wp-block-quote is-layout-flow wp-block-quote-is-layout-flow\">\n<p class=\"wp-block-paragraph\"><strong>\u23f3 Important \u2013 SCANPST May Appear Frozen:<\/strong> For very large PST files, SCANPST can take a long time and may look like it\u2019s \u201cNot Responding\u201d or frozen. <strong>Do not cancel it<\/strong>. Let it run\u2014it could take 30 minutes or more. Canceling mid\u2011process can corrupt the file further.<\/p>\n<\/blockquote>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h3 class=\"wp-block-heading\">7. Create a New Outlook Profile<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">Sometimes the profile itself becomes corrupted. A fresh profile can improve performance even after you\u2019ve shrunk the PST.<\/p>\n\n\n\n<ol start=\"1\" class=\"wp-block-list\">\n<li>Close Outlook.<\/li>\n\n\n\n<li>Go to <strong>Control Panel<\/strong> \u2192 <strong>Mail (Microsoft Outlook)<\/strong> \u2192 <strong>Show Profiles<\/strong>.<\/li>\n\n\n\n<li>Click <strong>Add<\/strong>, create a new profile, and add your email account.<\/li>\n\n\n\n<li>Under <strong>When starting Microsoft Outlook<\/strong>, select <strong>Prompt for a profile<\/strong>.<\/li>\n\n\n\n<li>Open Outlook with the new profile and test performance.<\/li>\n<\/ol>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h3 class=\"wp-block-heading\">8. Use the Microsoft Support and Recovery Assistant (SaRA)<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">SaRA can automatically diagnose and fix PST\u2011related issues.<\/p>\n\n\n\n<ol start=\"1\" class=\"wp-block-list\">\n<li><strong><a href=\"https:\/\/aka.ms\/SaRA-Outlook\" target=\"_blank\" rel=\"noreferrer noopener nofollow\">Download the Microsoft Support and Recovery Assistant<\/a><\/strong>.<\/li>\n\n\n\n<li>Run the tool and select <strong>Outlook<\/strong> \u2192 <strong>Outlook is slow or freezes<\/strong>.<\/li>\n\n\n\n<li>Follow the prompts. The tool can help with PST size, corruption, and add\u2011ins.<\/li>\n<\/ol>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\"><strong>Related Reading from Mukunda Software Updates<\/strong><\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">If you\u2019re troubleshooting other Outlook issues, these guides from our blog may help:<\/p>\n\n\n\n<div class=\"wp-block-columns is-layout-flex wp-container-core-columns-is-layout-8f761849 wp-block-columns-is-layout-flex\">\n<div class=\"wp-block-column is-layout-flow wp-block-column-is-layout-flow\">\n<figure class=\"wp-block-embed is-type-wp-embed is-provider-mukunda-software-updates wp-block-embed-mukunda-software-updates\"><div class=\"wp-block-embed__wrapper\">\n<blockquote class=\"wp-embedded-content\" data-secret=\"ubK0K3HYK0\"><a href=\"https:\/\/mukundasoftware.com\/blog\/help\/outlook\/fix-required-authentication-broker-missing-outlook.html\">Fix: \u201cA Required Authentication Broker is Missing\u201d in Outlook &amp; Microsoft 365<\/a><\/blockquote><iframe loading=\"lazy\" class=\"wp-embedded-content\" sandbox=\"allow-scripts\" security=\"restricted\" style=\"position: absolute; visibility: hidden;\" title=\"&#8220;Fix: \u201cA Required Authentication Broker is Missing\u201d in Outlook &amp; Microsoft 365&#8221; &#8212; Mukunda Software Updates\" src=\"https:\/\/mukundasoftware.com\/blog\/help\/outlook\/fix-required-authentication-broker-missing-outlook.html\/embed#?secret=ymHAEC1mJU#?secret=ubK0K3HYK0\" data-secret=\"ubK0K3HYK0\" width=\"600\" height=\"338\" frameborder=\"0\" marginwidth=\"0\" marginheight=\"0\" scrolling=\"no\"><\/iframe>\n<\/div><\/figure>\n<\/div>\n\n\n\n<div class=\"wp-block-column is-layout-flow wp-block-column-is-layout-flow\">\n<figure class=\"wp-block-embed is-type-wp-embed is-provider-mukunda-software-updates wp-block-embed-mukunda-software-updates\"><div class=\"wp-block-embed__wrapper\">\n<blockquote class=\"wp-embedded-content\" data-secret=\"jEYMrnJ8AJ\"><a href=\"https:\/\/mukundasoftware.com\/blog\/help\/outlook\/fix-msoutlook-folders-disappeared-only-inbox-visible.html\">Fix: MS Outlook Folders Disappeared (Only Inbox Visible)<\/a><\/blockquote><iframe loading=\"lazy\" class=\"wp-embedded-content\" sandbox=\"allow-scripts\" security=\"restricted\" style=\"position: absolute; visibility: hidden;\" title=\"&#8220;Fix: MS Outlook Folders Disappeared (Only Inbox Visible)&#8221; &#8212; Mukunda Software Updates\" src=\"https:\/\/mukundasoftware.com\/blog\/help\/outlook\/fix-msoutlook-folders-disappeared-only-inbox-visible.html\/embed#?secret=CbUWabEHhL#?secret=jEYMrnJ8AJ\" data-secret=\"jEYMrnJ8AJ\" width=\"600\" height=\"338\" frameborder=\"0\" marginwidth=\"0\" marginheight=\"0\" scrolling=\"no\"><\/iframe>\n<\/div><\/figure>\n<\/div>\n<\/div>\n","protected":false},"excerpt":{"rendered":"<p>TL;DR: Outlook performance degrades sharply when your PST file exceeds 20GB. The solution is to compact, split, or archive your data. Jump to Solution 3 to learn how to split your PST file safely. Few things test your patience like a sluggish Outlook\u2014endless \u201cNot Responding\u201d messages, delayed send\/receive, and random crashes. If your Outlook has &#8230; <a title=\"Fix: MS Outlook Runs Slowly or Crashes \u2013 Oversized PST File Performance\" class=\"read-more\" href=\"https:\/\/mukundasoftware.com\/blog\/help\/outlook\/fix-msoutlook-runs-slowly-or-crashes-oversized-pst-file-performance.html\" aria-label=\"Read more about Fix: MS Outlook Runs Slowly or Crashes \u2013 Oversized PST File Performance\">Read more<\/a><\/p>\n","protected":false},"author":4,"featured_media":2324,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[49],"tags":[],"class_list":["post-2323","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-outlook"],"_links":{"self":[{"href":"https:\/\/mukundasoftware.com\/blog\/wp-json\/wp\/v2\/posts\/2323","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/mukundasoftware.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/mukundasoftware.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/mukundasoftware.com\/blog\/wp-json\/wp\/v2\/users\/4"}],"replies":[{"embeddable":true,"href":"https:\/\/mukundasoftware.com\/blog\/wp-json\/wp\/v2\/comments?post=2323"}],"version-history":[{"count":2,"href":"https:\/\/mukundasoftware.com\/blog\/wp-json\/wp\/v2\/posts\/2323\/revisions"}],"predecessor-version":[{"id":2326,"href":"https:\/\/mukundasoftware.com\/blog\/wp-json\/wp\/v2\/posts\/2323\/revisions\/2326"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/mukundasoftware.com\/blog\/wp-json\/wp\/v2\/media\/2324"}],"wp:attachment":[{"href":"https:\/\/mukundasoftware.com\/blog\/wp-json\/wp\/v2\/media?parent=2323"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/mukundasoftware.com\/blog\/wp-json\/wp\/v2\/categories?post=2323"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/mukundasoftware.com\/blog\/wp-json\/wp\/v2\/tags?post=2323"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}