Comment by st_goliath

For a bit of context/back-story, Richard, who opened this issue, later also wrote a blog post about the whole ordeal:

https://blog.sigma-star.at/post/2022/07/protonmail-adventure...

In short: The idea was to move from a custom mail server to a paid, hosted solution. ProtonMail was chosen, with the bridge being used to get mails into a local mail client. Issues with the bridge eventually cropped up.