@ikonoklast

The concept of sealed sender is actually already implemented in DeltaChat

Sealed sender is a system where a receiver builds a connection with the sender, exchange a shared knowledge, and the the sender uses that shared kosnowledge to "authenticate" and be allowed to send content to the receiver. In deltachat you are encouraged to use as many profiles as you want, they are free to create. An equivalent flow is then:
- sender creates a new, ephemeral profile and creates a trusted connection with receiver (through qr-code or through the existing, trusted connection). Both sender's profiles are unrelated
- sender sends messages with that new profile. From the outside there is no way to link with old profile, it's a different address and more importantly a different key

It requires a bit more manual operations but it's there already. Use profiles, they're good stuff !
@delta