Egregoros

@drwho @ohmu @doraii Proton's business is a service that tries to be multiple things: encrypted messaging, but also still email, but interoperability is... not really there, so everyone has to be in this giant honeypot. By their very nature it's pretty centralized and there isn't much of an off-ramp available.

If you want to exchange private messages (and attachments) and really want SMTP to be the transport just use DeltaChat. It's free and federated.