when creating new profile in client, ask for all messages up to 5 days in past. In mail server, if we receive a timestamp in future from client, sync from 5 days in the past so that we send the client a message to update it's sync_time to our time (in the worst case, if they are no messages in the past 5 days, the client will still be able to send messages and receive them back, since we also update the local sync_time on the mail server side).