[contactlight11]

Well, the messages are not syncing from phone to desktop. They're syncing from the server to desktop. Need proof? Turn your phone off any access signal desktop. The messages exist in separate "mailboxes" on the server, one per linked device, and deliver independently. The timeout is 60 days if I recall correctly, for messages to be deleted from the server if they were not delivered to the client. Can't find the better source I know exists at this moment, see here for now: https://news.ycombinator.com/item?id=15596980