Multi user email service app

Seeking a dev to develop a multi-user application for an email service.

The ideal candidate should have knowledge of the user experience in messaging platforms. We’re seeking a relational database-linked app where users can signup, log in, and send emails. A service much like Gmail, Proton Mail, etc. Additionally, an admin dashboard to manage users and services.

Please respond with relevant examples and fixed price quotes. Preferably with links to hosted apps that are accessible.