I don’t see a way to implement the “Blind Group” type so an alternative could be a “Channel” group type, in the email the “To” header is set to the channel owner and the rest of the channel members are set in BCC, the channel owner is the only one who knows the group members and the only who can write in this group, users can only leave the channel, which will be shown as a channel in delta and shouldn’t let users to send anything, the bottom bar should be hidden