The use case for allowing 1:1 DMs to be exchanged via courier is to maximize OpSec for whatever messages are being exchanged - I may trust Bob to deliver a message, but Bob may not need to know the message content.
The feature could include marking "approved couriers" per contact, perhaps? Both Alice and Charlie would have to set Bob as an approved courier for message exchange to each other.
The use case for allowing 1:1 DMs to be exchanged via courier is to maximize OpSec for whatever messages are being exchanged - I may trust Bob to deliver a message, but Bob may not need to know the message content.
The feature could include marking "approved couriers" per contact, perhaps? Both Alice and Charlie would have to set Bob as an approved courier for message exchange to each other.