What are some alternatives?
Mailpile - Mailpile is a modern, fast web-mail client with user-friendly encryption and privacy features.
Hiver - Manage Customer Support, Sales and Projects right from your Gmail inbox. Collaborate with Shared Labels, Shared Contacts, email notes, email reminders and email templates
Roundcube - Web-based IMAP email client
CleanEmail - CleanEmail is an online service that empowers you to take control of your mailbox.
NeutronMail - Self-hosted server for the ProtonMail client.
MailClark - The Slack bot for external communications