I like toggling the star to indicate which emails I need to respond to more urgently, but I think it would be helpful to allow options in addition to the yellow star. Gmail, for example, allows yellow stars, red stars, orange stars, green stars, blue stars, purple stars, green checkmarks, red exclamation points, yellow exclamation points, a blue information symbol, a purple question mark, and an orange guillemet (the >> symbol). Allowing options such as this (I'd particularly love a dollar sign to flag bills and receipts) would really make stars more useful by letting us use different colors and symbols as easy but clear ways of differentiating between different categories of email or reminding us to do different things with them.