How would people design a resilient mail server setup with Linux?

On an application level what the system needs to provide is both an incoming and outgoing mail service (i.e. SMTP & IMAP), along with filtering and archive storage (the archive part isn't critical yet, so we'll look at this later probably).

What is required on top of this is a resilient system, i.e. one which will handle individual server failures without interrupting service. As such I would term this a High Availability mail system. This is in contrast to a High Performance mail setup, as in our case the volume of mail being handled isn't the important factor, it's simply that it stays online.

Having not approached this problem before, the first thing I thought of was a clustered file system (gfs/gluster/etc), combined with heartbeat to failover a floating IP to another box in the case of a server failure.

Combined with postfix & dovecot does this sound feasible to people?