I have just upgraded my system to xubuntu 16.04 (from 15.10). It all went very smoothly.
However the new (presumably) mutt which is 1.5.24 has a very annoying quirk. It switches the terminal to reverse video when it exits. It appears to be the 'Mailbox is unchanged' (or whatever else is output when I leave) that does the change. I have 'light on dark' terminal windows and mutt seems to want it to be the other way round. -- Chris Green