Full description
Proton Mail Bridge has been open-source since April 2020.
It functions as a daemon that serves as an interface between Proton
Mail's encrypted email services and standard IMAP/SMTP email clients.
This allows users to integrate Proton Mail with applications like
Thunderbird, Outlook, and Apple Mail.
The Bridge can be compiled with or without its Qt-based graphical
user interface (GUI), offering flexibility for both desktop and
headless environments.