Little add-on to keep Outlook running when clicking on the exit button
Credit goes to @Tim Eck on Superuser (https://superuser.com/users/78284/tim-eck) I'm just reuploading it on GitHub to back it up, this add-on works for Outlook 2010, 2013, 2016, 2019 and Outlook 365.
To exit Outlook after installing the add-on use File -> Exit
PS: In case the sourceforge.net link goes down, I add the .dll file to the project so you can get it from here