Using New Outlook on Windows for personal email, calendar, and contact management
Ok, there is a way to change this setting. First, open a new email draft, then click on Options. The first button on the ribbon should be "Editor."
If the "Editor" button is greyed out, you need to enable it.
Go to settings using the gear in the upper right hand corner
Click on General>Privacy and Data
Scroll to the bottom and click on Privacy Settings
Scroll down to Connected Experiences
Make sure both options are turned on.
Close out MS Outlook and restart.
Editor Enabled
Open new email draft, click on Options tab
Click on Editor pulldown and select Editor Settings
Here you can disable/turn off Auto Capitalization
Click OK