Top 12 mailcow dockerized Alternatives

A fully fledged, free email server solution, an open source project (GPL v2).

Web-based IMAP email client

Zimbra Collaboration is an open, secure collaboration tool for email, calendaring, tasks and more.

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.

Horde Groupware is a free, enterprise ready, browser based collaboration suite.

Mailpile is a modern, fast web-mail client with user-friendly encryption and privacy features.

RainLoop is a web based email client.

Modoboa is a mail hosting and management platform including a modern and simplified Web User Interface.

SquirrelMail is a standards-based webmail package written in PHP.

All your E-mail, from all your accounts, in one place. Cypht is like a news reader, but for E-mail.

Kolab Groupware is a secure, scalable, reliable, flexible, full-featured collaboration suite.

Google's encompassing suite of cloud-based business apps.