I just posted a new Outlook sample on GitHub. I have created something very similar to this sample for a couple of customers now and have been using this as a template. What this sample does is place a button on the Ribbon for users to report suspicious email to the administrator. The user will get the option to select why they think it is suspicious as well as provide a comment. When they click Send, it will email the administrator. The email address which receives this notification is configured in the URL for the add-in page via the manifest XML.
Anyway, I wanted to share this basic sample with the community so others can use this to quickly implement similar solutions in their environment.
All the details for configuring the add-in are in the README.md. Here is the link the new sample: https://github.com/davecra/Outlook.ReportAddin. I also created this in VS Code.
Please let me know if you have any questions or suggestions for other samples you would like to see.