How to add a button to a pre-existing tab on ribbon (C#)?

Question

I\'ve successfully created a new tab and put it next to the pre-existing ones. Then I realized that I\'ll only have one button on it, so it makes more sense (for now) to put it

Answer 1

For people frustrated that none of the other answers seem to be working, go to the properties for the Ribbon itself and set the RibbonType to Microsoft.Outlook.Explorer (or whichever context[s] you want to see the control in). It's a crucial step that's easy to overlook.

Then follow the other instructions to set OfficeId to TabMail.

Additionally, Office 2016 Fluent Control Identifiers can be found here: https://www.microsoft.com/en-us/download/confirmation.aspx?id=50745