I have created a custom Add-In for 2007/2010 and 2013. The addin - custom control appears well and neatly each time a new window is opened up / popuped. We can see the ribbon in the "Message Tab".
However if we try to an in-line or in response in 2013. The ribbon doesnt appear in the ribbon.
The development is all done using the VSTO code. (Am not looking for any 3rd party tool) I cannot switch over to XML based control at this stage.