Airmail is described as 'Lightweight mail client supporting multiple accounts, customizable actions, unified inbox, Smart Inbox filtering, privacy mode, and send later scheduling' and is a popular Email Client in the office & productivity category. There are more than 50 alternatives to Airmail for a variety of platforms, including Mac, Windows, Linux, Android and iPhone apps. The best Airmail alternative is Thunderbird, which is both free and Open Source. Other great apps like Airmail are K-9 Mail, Evolution, Microsoft Outlook and Spark Mail.
It is so different I had trouble adjusting. There is no snooze or swipe.