This article explains how to minimize Outlook to the system tray in Windows 10. The instructions apply to Microsoft Outlook 2019, Outlook 2016, Outlook 2013, Outlook 2010, and Outlook for Microsoft 365.
How to minimize Outlook to the system tray
If your Windows taskbar is getting too cluttered, but you'd rather keep Microsoft Outlook open at all times, you can add an Outlook icon to the system tray.
Go to the Windows system tray and right-click on the Outlook icon.
Select Hide on minimize. A check mark for Hide on minimize indicates that Outlook is set to minimize to the system tray.