What are some alternatives?
Roundcube - Web-based IMAP email client
Rainloop - RainLoop is a web based email client.
Jam.py Postfix Aliases - Web App to manage only Postfix Aliases with a LARGE number of managed Domains (>hundreds).
Horde - Horde Groupware is a free, enterprise ready, browser based collaboration suite.
Mailpile - Mailpile is a modern, fast web-mail client with user-friendly encryption and privacy features.
mailcow dockerized - An open source mailserver suite.