This method will guide you to create a search folder to collect all unread items from the specified folder and its subfolders, and then show the total number of unread items in the search folder in Outlook.

1. Select the folder that you will show the number of unread items including the subfolders, and click Folder > New Search Folder.

2. In the New Search Folder, please click to highlight the Create a custom Search Folder option, and click the Choose button.

3. In the opening Custom Search Folder dialog box, please type a name for this new search folder in the Name box. See screenshot below:

4. Click the Criteria button to open the Search Folder Criteria dialog box, next go to the More Choices tab, check the Only items that are option, select unread from right drop down list, and click the OK button. See screenshot above:

5. Now you return to the Custom Search Folder dialog box. Please click the Browse button to open the Select Folder(s) dialog box; next check the specified folder and Search subfolders option, and click the OK button. See screenshot:

6. Click OK > OK buttons to save the settings.

Now the new search folder is added in the Navigation pane, and the number beside the search folder indicates the total number of unread items in the specified folder and its subfolders. See screenshot:

If you have Kutools for Outlook installed, you can apply its Statistics feature to quickly show the total number of all unread items in a folder including its subfolders in Outlook. Please do as follows: Note: This Statistics feature is new in Kutools for Outlook 8.00 which is being tested and will be released sooner.

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1. Click Kutools Plus > Statistics.

2. In the first Statistic dialog box, please only check the folder that you will count the total number of unread items including its subfolders, and click the OK button.
Note: By default, all folders are checked in the Statistics dialog box. You can uncheck them with right clicking any folder and selecting Uncheck All from the context menu.

And then you will see the total number of all unread items in the specified folder and its subfolders display at the top of the second Statistics dialog box. See screenshot:

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