What are some alternatives?
When comparing Mail-in-a-box and mailcow dockerized, 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!
iRedMail - A fully fledged, free email server solution, an open source project (GPL v2).
Mailbird - Mailbird is the best email client for Windows 7, 8 and 10
Zimbra Collaboration Suite - Zimbra Collaboration is an open, secure collaboration tool for email, calendaring, tasks and more.
Postbox - The Power Email App for busy professionals, like you.
Modoboa - Modoboa is a mail hosting and management platform including a modern and simplified Web User Interface.