hydroxide

Free ProtonMail bridge for using with any email client you prefer

Hydroxide is a free, third-party and open-source ProtonMail bridge for using with any email client of your choice. Hydroxide is a server meant to be run in the background, supporting IMAP and SMTP that translates standard protocols (SMTP, IMAP, CardDAV) into ProtonMail API requests. Hydroxide stores each of your account credentials in a json file located in /var/db/hydroxide by default as encrypted form, then uses .db files per account for other purposes.