Airmail for the Mac is all set to take on the new features of El Capitan and possibly even iOS with its latest update. It now supports features like split screen and has preference syncing via iCloud. It even now has support for Handoff, too. The app also now supports native integration of Wunderlist and Todoist. Plus, it gets a bit of an interface redesign, too.
Source: Lifehacker | Download: iTunes App Store ($11.99)