You can limit the synchronization window that’s used for calendar folders to reduce the number of items that are stored locally in your calendar folders. Use the Turn on shared calendar improvements option for users who have edit permissions to a shared calendar to improve performance. When you enable this option, calendar actions are sent directly to the server instead of having to be synchronized from local storage. I even reduced mailboxes sizes and that didn't help, I setup a new user (albeit existing PC but new windows profile), and he is having the same issues. If the mailboxes open automatically after removing them and restarting Outlook, they may be auto mapped. This setting can be changed by an Exchange admin by submitting a https://fixoutlookhelp.wordpress.com/2025/10/29/repair-outlook-ost-and-pst-files-2025-guide/ request via Jira and including the usernames of the client and the usernames of the mailboxes that need to be removed.
The root cause was the deployment of an incorrect campaign data file, which led to false positive campaign detection. We have since reverted to the right data file and the outbound email flow has returned to a normal state. We also released a new rule that corrected the wrong campaign verdict for all impacted customers during the incident. If you're having problems sending or receiving email, read how to Fix Outlook.com email sync issues. If you've successfully sent and received email from classic Outlook before, and now Outlook repeatedly asks you to reenter your password, one of two things may have happened.
After you run any troubleshooter, Get Help provides details on any findings and suggestions for possible remedies. If one of these resolves your problem, close https://fixoutlookhelp.wordpress.com/2025/10/29/repair-outlook-ost-and-pst-files-2025-guide/ the app and continue working. If you can't open Outlook, or Outlook disappears or crashes, one of your add-ins may be to blame or you may need to update Outlook. Under Calendars, My calendar is the default selection and displays the calendar in Month view.
If so, wait a short time (usually two or three minutes) to see if Outlook starts working again. Visit the small business help & learning page to learn how you can use Outlook and other Microsoft 365 apps and services in your small business. There is currently no option to revert https://fixoutlookhelp.wordpress.com/2025/10/29/repair-outlook-ost-and-pst-files-2025-guide/ to the prior behavior, but we would love to hear your feedback to help us with future designs. To learn more about how to send us feedback, please see How do I give feedback on Microsoft Office.
Set up your account manually as an IMAP or POP account in Outlook. Customers using the contact support buttons at the foot of the support pages, or the "email us" links in support Virtual Agent, are unable to open the Help Pane. You can also Sign out manually then close all browser windows. Check that you have not accidentally blocked the Gmail domain when blocking one Gmail user. While we fix the problem, you can send the file as a OneDrive link.
If you try to perform other actions while Outlook is in use, Outlook may not respond. Let the task in process finish its job before you try another action. Make sure that the latest updates for Outlook are installed. For more information, see How to install the latest applicable updates for Microsoft Outlook (US English only).
Serious problems might occur if you modify the registry incorrectly. Before you modify it, back up the registry for restoration in case problems occur. The settings in the Send/Receive Group windows let you customize the synchronization rate of the new group. The software can be deployed in virtual, hosted cloud, on-premises, or hybrid network environments. The company sells its software and services directly and through a network of global channel partners. Before using this tool, we recommend making a backup copy of your PST file in case any errors or file corruptions occur to the original file.
Whether it’s creating a new outlook profile or setting up your primary email, we’ve got you covered. Sometimes a Windows update or app update—meant to fix things—ends up causing the problem. Especially if you’re using a different version of Windows, this can break compatibility with Microsoft Outlook or Outlook configuration files. If Outlook still misbehaves, your antivirus might be https://fixoutlookhelp.wordpress.com/2025/10/29/repair-outlook-ost-and-pst-files-2025-guide/ the culprit.
Having trouble connecting to your email from Outlook on your desktop? Follow these steps to let Outlook diagnose and fix errors in your Outlook mail profile that might be causing the issue. To get support in Outlook.com, click here or select Help on the menu bar and enter your query. If the self-help doesn't solve your problem, scroll down to Still need help?
For more information about when builds are available for their respective channels, go to Update history for Microsoft 365. We're investigating the issue and will update this page when a fix is available. 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. 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. If you're using Outlook 2010, Outlook 2013 or Outlook 2016, uninstall and re-install iCloud to resolve this issue.
The root cause was the deployment of an incorrect campaign data file, which led to false positive campaign detection. We have since reverted to the right data file and the outbound email flow has returned to a normal state. We also released a new rule that corrected the wrong campaign verdict for all impacted customers during the incident. If you're having problems sending or receiving email, read how to Fix Outlook.com email sync issues. If you've successfully sent and received email from classic Outlook before, and now Outlook repeatedly asks you to reenter your password, one of two things may have happened.
After you run any troubleshooter, Get Help provides details on any findings and suggestions for possible remedies. If one of these resolves your problem, close https://fixoutlookhelp.wordpress.com/2025/10/29/repair-outlook-ost-and-pst-files-2025-guide/ the app and continue working. If you can't open Outlook, or Outlook disappears or crashes, one of your add-ins may be to blame or you may need to update Outlook. Under Calendars, My calendar is the default selection and displays the calendar in Month view.
If so, wait a short time (usually two or three minutes) to see if Outlook starts working again. Visit the small business help & learning page to learn how you can use Outlook and other Microsoft 365 apps and services in your small business. There is currently no option to revert https://fixoutlookhelp.wordpress.com/2025/10/29/repair-outlook-ost-and-pst-files-2025-guide/ to the prior behavior, but we would love to hear your feedback to help us with future designs. To learn more about how to send us feedback, please see How do I give feedback on Microsoft Office.
Set up your account manually as an IMAP or POP account in Outlook. Customers using the contact support buttons at the foot of the support pages, or the "email us" links in support Virtual Agent, are unable to open the Help Pane. You can also Sign out manually then close all browser windows. Check that you have not accidentally blocked the Gmail domain when blocking one Gmail user. While we fix the problem, you can send the file as a OneDrive link.
If you try to perform other actions while Outlook is in use, Outlook may not respond. Let the task in process finish its job before you try another action. Make sure that the latest updates for Outlook are installed. For more information, see How to install the latest applicable updates for Microsoft Outlook (US English only).
Serious problems might occur if you modify the registry incorrectly. Before you modify it, back up the registry for restoration in case problems occur. The settings in the Send/Receive Group windows let you customize the synchronization rate of the new group. The software can be deployed in virtual, hosted cloud, on-premises, or hybrid network environments. The company sells its software and services directly and through a network of global channel partners. Before using this tool, we recommend making a backup copy of your PST file in case any errors or file corruptions occur to the original file.
Whether it’s creating a new outlook profile or setting up your primary email, we’ve got you covered. Sometimes a Windows update or app update—meant to fix things—ends up causing the problem. Especially if you’re using a different version of Windows, this can break compatibility with Microsoft Outlook or Outlook configuration files. If Outlook still misbehaves, your antivirus might be https://fixoutlookhelp.wordpress.com/2025/10/29/repair-outlook-ost-and-pst-files-2025-guide/ the culprit.
Having trouble connecting to your email from Outlook on your desktop? Follow these steps to let Outlook diagnose and fix errors in your Outlook mail profile that might be causing the issue. To get support in Outlook.com, click here or select Help on the menu bar and enter your query. If the self-help doesn't solve your problem, scroll down to Still need help?
For more information about when builds are available for their respective channels, go to Update history for Microsoft 365. We're investigating the issue and will update this page when a fix is available. 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. 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. If you're using Outlook 2010, Outlook 2013 or Outlook 2016, uninstall and re-install iCloud to resolve this issue.