The whole point of end-to-end encryption is that you shouldn't have to.
The entire point of Sealed Sender and their use of zero-knowledge proofs for group membership is so the server doesn't know who's talking to who, so they can't even selectively censor messages from one person.
The entire point of Sealed Sender and their use of zero-knowledge proofs for group membership is so the server doesn't know who's talking to who, so they can't even selectively censor messages from one person.