Add "Starred Messages" to the sidebar
I think it might be useful to have a "Starred Messages" entry in the sidebar that, when selected, shows only starred messages. Right now, starring a message isn't particularly useful. I star it in Geary, which adds a star icon... and that's pretty much it. I'm not sure what else Starred Messages are supposed to do, but at least having a sidebar entry for it would allow them to be seen/managed.
I mentioned this is another report I submitted, but if the "Starred Messages" could sync with Fastmail's pinned emails, that'd be super awesome and a huge bonus.