What are some alternatives?
CleanEmail - CleanEmail is an online service that empowers you to take control of your mailbox.
Roundcube - Web-based IMAP email client
Dimelo Mail - Dimelo Mail is a software that manage inbound emails.
mailcow dockerized - An open source mailserver suite.
WP Mailster - WP Mailster enables you to run a listserv-like email discussion list on your WordPress site.
Mailpile - Mailpile is a modern, fast web-mail client with user-friendly encryption and privacy features.