What are some alternatives?
When comparing Apple Mail and OpenMailBox, you can also consider the following products
Thunderbird - Thunderbird is a free email application that's easy to set up and customize - and it's loaded with great features!
ProtonMail - Secure email with absolutely no compromises. Get your free encrypted email account today.
eM Client - eM Client is a Windows-based email client for sending and receiving emails, and managing calendars, contacts and tasks.
Tutanota - Get your encrypted mailbox for free.
Mailbird - Mailbird is the best email client for Windows 7, 8 and 10
Gmail - Gmail is a free search-based web-mail service.