Spark is unique because it includes a "Smart Inbox" that's able to filter emails to show you the most unread important messages first. It's able to tell if an email is personal, a notification, or a newsletter, processing it accordingly. It's designed to let users check to see if an email is important at a glance.
Like many iOS mail apps, Spark uses swipes to quickly delete and archive incoming emails. It includes a pinning feature (stars in Gmail) to denote tasks that need to be completed immediately, and there's a snooze feature for putting off emails until another day. Built-in quick replies let users reply to messages with pre-selected messages, a feature that's useful on the Apple Watch, and there's a smart search for finding messages based on name and time frame.
Spark's update optimizes the app for all screen sizes, from iPhone to iPad, and it includes a revamped design. Other new features include additional languages (English, German, Chinese Russian, Spanish, French, Italian, Japanese, and Portuguese are available) and support for watchOS 2.
Readdle is also working on a Spark app for the Mac, but the company says "it will take some time" to create "the best email client for Mac out there."
Spark can be downloaded from the App Store for free. [Direct Link]