In Sync Window Settings, adjust the number of months of data that are synced for the primary shared calendars. (For example: Any item that is not modified within one year moves to the Deleted Items folder.) Method 3 Method 2Īpply a Retention Policy on the Calendar folder to delete items from this folder. If you have enabled Online Archive Mailbox, archive items to the Online Archive Mailbox. If you have exceeded the recommended limit of 5,000 total Calendar items, use any of the following methods to reduce the number of items that you have. Optionally, if you have a Microsoft Exchange online archive, you can move items to that archive. ost) file, move items from the larger folders to separate or smaller folders in the same mailbox or data file. If you have folders that exceed the limit for the number of items in an Outlook data (.pst) file or an offline Outlook data (. Before you modify it, back up the registry for restoration in case problems occur. Serious problems might occur if you modify the registry incorrectly. The limits for Outlook 2019, Outlook 2016, Outlook 2013, and Outlook 2010 are as follows:įollow the steps in this section carefully. This problem might occur if you have folders that exceed the limit for the number of items per folder or if you have too many folders total.

This behavior occurs because it takes a long time to enumerate the folders. In extreme cases, if there are more than 10,000 folders, Outlook is very slow to open.Additionally, errors are logged in the Sync Issues folder and '9646' events are logged in the Application log. If your Outlook profile has shared mailboxes and has caching enabled ( Download Shared Folders is selected), folder synchronization issues, performance issues, and other problems occur if the number of shared folders per mailbox exceeds 500, as described in Performance and synchronization problems when you work with folders in a secondary mailbox in Outlook.

Folders are not displayed correctly, or they take a long time to appear, especially in cached mode.If you have lots of mail folders, you might experience performance issues such as the following: For example, meeting updates might not be reflected in the primary, shared, or delegated calendar. You experience decreased performance in Outlook if the Inbox, Calendar, Tasks, Sent Items, or Deleted Items folders contain lots of items.When you use Cached Exchange Mode or an Outlook data (.pst) file, you notice performance issues when you do certain actions.If you have lots of items in any single folder, you might experience symptoms such as the following in Microsoft Outlook:

Outlook 2016 sync issues folder crash