Today I learned from Level2 Support that the error "Outlook not installed" "Install Outlook client on your system to select this option",  even when Outlook is sitting in plain view, can happen if the Outlook is not "installed locally (from a CD/DVD)". If the Outlook is web-installed, "sometimes" QuickBooks will not recognize it. In that event, configure the sender(s) email address and password with the third option "Add".