It supports all the usual services: Gmail, iCloud, Hotmail, Yahoo, and IMAP. It has a really great interface on both Mac and iOS. It’s incredibly clean, fast and has tons of features. It has integrations with services like Todoist, Pocket, Instapaper, Evernote, and Wunderlist. It also supports snoozing and read receipts.
The app is free to download, but there is a $49.99 annual subscription fee to use the app. If we want to avoid another Sparrow situation, this is likely the best route. They have a free trial, so I recommend you give it a shot.