Using New Outlook on Windows for professional communication and productivity
Hi Allard,
Since you're using New Outlook, you can sort them to alphabetical order, go to View > Folder Pane and select Sort Folders > Order folders A to Z.
You can also customize the order of your folders
- From the navigation in new Outlook, select Mail
Select the View tab on the ribbon, select Folder pane
Select and hold the folder you want to move, and then drag and drop it to the new location.
Or, right-click the folder and select Move up or Move down.

When the Custom folder order option is selected, you also have the option to move folders from the main level into subfolders and vice versa.
For your references: Change the order of folders in the Folder Pane in Outlook - Microsoft Support
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