您在对话中有参与者(您称其为字母).

You have the participants in conversations (you call it letters).

只需过滤当前用户，您就会好起来.

Just filter the current user and you'll be good.

conversation = user.mailbox.sentbox.first
filtered_participants = conversation.participants.reject do |u| 
  u.id == current_user.id
end