Configuring preferences and options in Outlook.com
I agree with the others on here that this behavior is extremely dangerous and a boon for cybercriminals. I have no idea why Microsoft would promote this behavior. This response from Microsoft is also not helpful as it is only for composing messages and not for the reading pane. Additionally, as others have pointed out this is for the web page, but on that page its not even accurate as there is no "Always show email address." box anywhere. There is an "Always show From" (the one I think they are referring to) and "Always show Bcc", but like I stated earlier, this is only for composing messages. If some clicks on a link in a phishing email, this is of no use at all.
Microsoft please be better.