Outlook inbox double click to open a unread not working

Hello, 
I came across your post since i had same issue i made some research. If you are using New Outlook, then this behavior cannot be disabled - this behavior of single click to open mail is actually a feature of the "New Outlook" and cannot be disabled (trust me, looked all over the settings :) You can select messages without opening them by using CTRL + left-click on the message, but this will just select the message, not what you are looking for. IF you prefer double clicking to open the message then i would recommend switching back to the Classic Outlook by toggling switch to Classic at the top right corner of your Outlook window. Classic Outlook has double-clicked to open as a default functionality i believe. Hope that helps! :)