Outlook 2016 should behave like a modern Mac application
Outlook should behave like a modern Mac application and remember all of the windows you previously had open when launching Outlook.
I frequently have 5 to 10 emails open in separate windows. Some are existing messages that I need to reply to and some are ones that I am currently replying to. And yes I know that the ones you are working on are saved as drafts and you can add reminders to work on others, etc. but if these windows aren't re-opened after I launch Outlook I will often forget I have drafts I am working on or forget emails that I need respond to. Adding reminders doesn't always help because I usually have an average of 50 reminders (appointments, tasks, emails) so that is not always helpful. Sometimes I also like to have my calendar open in a separate window so I can look at emails and appointments side-by-side.
The other reason this would be useful is that when Outlook updates are available (which is now much more frequent with Office 2016's monthly updates) I am usually reluctant to apply the latest updates until I have processed all of the email windows I have open (which sometimes is many days later). If Outlook remembered all of the windows I have open along with window placement like a modern application I would be more likely to apply updates sooner. For the same reason I often delay OS security updates until I have processed all of my open windows.