Seeking to add custom items to context menu

[simonm]

I am using VS2015 and trying to create an outlook addin to add custom context menu items (when a user right-clicks on a mail item for instance). I have read this article:

https://msdn.microsoft.com/en-us/lib...or=-2147217396

However, I cannot get the GetCustomUI method to fire. Here is my code:

Public Class ThisAddIn
    Implements Microsoft.Office.Core.IRibbonExtensibility

    Private WithEvents myApp As Outlook.Application

    Private Sub ThisAddIn_Startup()
        Try
            myApp = Me.Application
        Catch ex As System.Exception
            Diagnostics.Debug.Print(ex.Message)
        End Try

    End Sub

    Private Sub ThisAddIn_Shutdown()

    End Sub

    Public Function GetCustomUI(RibbonID As String) As String Implements IRibbonExtensibility.GetCustomUI
        Diagnostics.Debug.Print(RibbonID)
        Return ""
    End Function

End Class

Can anyone help me find what I might be missing?