Great search and snooze functions, as well as a terrific Smart Inbox. Furthermore, the UI has everything I look for in an email application.

Folders are created per email address, so you can't save an email from one address to another one's folder in the phone app.

Ever since Mailbox became a graveyard app, I have been looking for a worthy replacement – and Spark is as close as it gets! The UI is clean, combining dark and light colors which helps with using the app; the side menu being dark while the rest of the UI has a white background makes you focus on the important stuff (the mail list and the mail in focus)!