I am using an open source Outlook add-in [Link], however, the add-in only appears on the Explorer ribbon (the main Outlook window), however, when I open an email it does not appear, I want to change this behavior so it appears in both Message/Read window and the Explorer window, I have read about RibbonType but what I believe that needs Visual Designer and this project does not use it, how can this be implemented?
The add-in project uses ribbon XML for customizing the Outlook UI. It seems you need to edit the Ribbon1.xml and Ribbon1.cs files to include the required customizations. Read more about the Ribbon UI (aka Fluent UI) in the following series of articles: