When you open Settings, System, you are initially placed in the left column allowing you to select the pane you want, though I can't know which one yours will open on if you've been there recently. Up and/or down arrowing should get you to "Notifications and Actions." You simply tab from there and it will go control by control through the pane. Of course, you can search for your e-mail client name, Outlook in this case, then tab over to its On/Off toggle, which will probably still be announced as a checkbox.
Of course, this is predicated on your having the toggle for Get notifications for apps and other senders ON. If that toggle is off then you do not have access to the individual apps/senders, as you've said that none should be allowed if it's OFF.
Brian - Windows 10 Home, 64-Bit, Version 1809, Build 17763
Explanations exist; they have existed for all time; there is always a well-known solution to every human problem — neat, plausible, and wrong.
~ H.L. Mencken, AKA The Sage of Baltimore