Hi, As new sup, but experienced vim user, I relatively quickly understood the 'modes' concept (although a short Wiki article would be helpful for novices).
However, it is confusing to me that the same key could have different meanings in different modes. As well, some keybindings seem redundant and increase complexity. E.g. '.s', ',s', ']s' are related to spam, but 's' could also mean 'save message'. 'S' is used for marking spam in one mode, and for searching contacts in a different mode.  
My suggestion would be to unify the keybindings in the different modes - i.e. to define more global keybindings - and to use unique ones where needed. Some keybindings are more confusing than helpful in my opinion. Thus, one option could be the definition of 'keybindings sets' (e.g. 'minimal', 'full') and/or an curses-menu for activating/ disabling keybindings (ideally, with custom entries). 

Best regards, 

Robert