Outlook performance is slow in Microsoft 365 Outlook Microsoft Learn

Outlook 2016 freezes when you try to preview an Excel file that’s attached to an email. MAPI does not validate that a provider’s DLL that it is requested to load is registered correctly in MapiSVC.inf or even that it comes from the local machine. why is Outlook not opening This can be exploited by creating a file together with an OLE object in such a way to cause MAPI to load a DLL from a network share when the OLE object is activated. The loading of unregistered MAPI services has been disabled by default to make Outlook more secure. This issue affects all Outlook versions on Windows 7, Windows 8, Windows 10. When you try to accept a shared Outlook.com calendar using your Microsoft 365 for business account in Outlook 2016, you might receive the “Something went wrong” error or your sign-in might fail.

Running the /resetnavpane command removes all customizations to the navigation pane. Starting Outlook in safe mode, which starts Outlook without add-ins loaded, can tell you if an add-in is the source of the problem. After October 14, 2025, Microsoft will no longer provide free software updates from Windows Update, technical assistance, or security fixes for Windows 10. Your PC will why is Outlook not opening still work, but we recommend moving to Windows 11.

If you have email messages in an email program, you must import your email messages and addresses to the new user profile before you delete the old profile. If everything is working correctly, you can now delete the old profile. Your user profile is a collection of settings that let you customize the computer appearance and performance.

When reaching why is Outlook not opening this point of the guide, the issue most likely also occurs for other users on the computer. This means that the issue is not caused by a configuration setting but by an installation error. If Outlook worked correctly the last time and nothing has changed about your account configuration, then checking if things work correctly in Safe Mode is a good first step. Starting Outlook in Safe Mode will prevent some or all add-ins from being loaded, prevents several settings files from being loaded and turns off the Reading Pane. Many users report common Outlook problems on Microsoft forums and support platforms. In this guide, we’ll walk you through practical, do-it-yourself solutions to troubleshoot and fix these issues so you can get back to work without delays.

If your antivirus software includes integration with Outlook, you may experience performance issues. You can disable all Outlook integration within the antivirus software. Or, you can disable any antivirus software add-ins that are installed in Outlook. This efficiently fixes the “Outlook freezes when sending email” error. Repairing your Office programs can resolve issues with Outlook not responding or freezing.

The original .ost file must be converted to a pst file using Recovery Toolbox for Outlook and then opened in Outlook. Conversion from OST to PST using Recovery Toolbox for Outlook doesn’t require the availability of Exchange Server or Windows Domain Controller. The full version of Recovery Toolbox for Outlook transforms it from a data loss diagnostic tool into a complete data recovery solution. It empowers you to identify recoverable data and restore it to a usable state within Outlook, giving you a much better chance of retrieving your critical information. You will be able to move on to the next recovery step (the Next button will become available), if the program finds more than one item in the source .pst file. When the search is over, select one of the files from the list in the central part of the search panel and click the OK button.

If it is required, check if there are other Outlook settings that could optimize its performance in Outlook. Upgrade to Microsoft Edge to take advantage of the latest features, security updates, and technical support. In some cases, an Outlook messaging profile may be misconfigured.

This issue occurs because Outlook cannot open the Forms Library. This issue can occur for Outlook on all Microsoft 365 Office channels. The emerging cases for this issue are on virtual desktop infrastructure (VDI). This is quite annoying and you’re certainly not alone. This should resolve the issue with Microsoft Outlook crashing. Perfectly repair and recover corrupted Outlook PST & OST files.

To open Outlook in Safe Mode, follow the instructions below. As @ode2joy ​ said, clearing out the user’s profile usually works, which is a more thorough procedure than just deleting .nst and .ost files. If a Microsoft 365 application such as Word or Excel isn’t working correctly, sometimes restarting it will fix the problem. When you’re done, you might need to restart your computer. You can determine if it’s corrupted by creating a new profile and changing which profile is used when Outlook starts. Use the classic Outlook for Windows connectivity troubleshooter to troubleshoot Outlook connectivity issues.

The issues documented in this section have been reported after installing the recent updates listed below. We’re investigating the issues and will update this page why is Outlook not opening when a fix is available. In the meantime, please use the workarounds suggested for each issue.