1- Plugin Observer : Identify the url from administration associated to the message.
It can be a precise url (a setting page from a component) or more global (for instance the list of the articles - url including "option=com_content").
Plug in Observer to be used : "URL Navigation"
2- Plugin Action : Message creation
Possibility to select specific users (or groups) for which the message is dedicated
Possibility to insert HTML (link, image, style).
Plug in Action to be used : "Message Popin"