There is a new tool available for Sparkers: ProtonMail Bridge
What is ProtonMail?
ProtonMail is the world’s largest encrypted email service with millions of users. ProtonMail offers encrypted email, which makes it virtually impossible for anyone to read it except the sender and the recipient.
What is ProtonMail Bridge?
ProtonMail Bridge is an application available to all paid users that enables the integration of your ProtonMail account with popular email clients, such as Microsoft Outlook, Mozilla Thunderbird, or Apple Mail. Bridge runs in the background by seamlessly encrypting and decrypting messages as they enter and leave your computer. The app is compatible with most email clients supporting IMAP and SMTP protocols.
Installation (Sparky 5 & 6 amd64):
sudo apt update
sudo apt install protonmail-bridge
License: GNU GPLv3