Redundant e-mail server

Is it possible have two exchange 2K servers on the same administrative group that work in redundency? In other words, I have two exchange servers on the same LAN and I’d like to synchronize them so that users are always able to login and use their e-mail. Is this can be done? Is this mean that a user need to have his mail-boxe stored in two different servers in the same time? ..mmmm sounds creazy?