When apple is the 9th largest corporation in the world, and that's competing with Big Oil and King Coal, I'm surprised that their mail.app is seen as so inferior by mac users?
https://en.wikipedia.org/wiki/List_of_largest_companies_by_revenue
Is it just not a priority? They have (according to the wiki) about $215 billion in annual revenue and 110,000 employees. Spark has 85 employees. Can someone explain why all the other features in the other apps that people have mentioned here are not already in Apple's mail.app, with bells on it?