I spend a lot of time in Outlook and I’ve found these shortcuts to be invaluable.
Ctrl+Shift+M : Open a new email window
Ctrl+Enter : Send the email that you’ve typed
Ctrl+Shift+I : Navigate to the Inbox from other folders
Ctrl+R : Reply to an email
Ctrl+Shit+R : Reply All
Ctrl+Shift+V : Move an email to another folder