Sender anonymity means that the server (or any recipient) cannot determine who sent a particular message. In your example, the centralized server absolutely knows which tweet-sized message was sent by each sender. So your proposal does not provide sender anonymity. Unless of course, the senders use an actual anonymity system to send their messages to the server...
Sender anonymity means that the server (or any recipient) cannot determine who sent a particular message. In your example, the centralized server absolutely knows which tweet-sized message was sent by each sender. So your proposal does not provide sender anonymity. Unless of course, the senders use an actual anonymity system to send their messages to the server...