What are some alternatives?
When comparing iRedMail and mailcow dockerized, you can also consider the following products
Zimbra Collaboration Suite - Zimbra Collaboration is an open, secure collaboration tool for email, calendaring, tasks and more.
Roundcube - Web-based IMAP email client
Modoboa - Modoboa is a mail hosting and management platform including a modern and simplified Web User Interface.
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.
Mail-in-a-box - Mail-in-a-Box provides webmail and an IMAP/SMTP server for use with mobile devices and desktop mail software and also includes contacts and calendar synchronization.