vqalive negotiates a shared ip between two machines. This provides for hot stand by failover to a redundant machine, thus increasing overall uptime.
Two identical email servers each have an IP assigned to them. A third "virtual" IP is shared between the two machines. vqalive manages which machine has the virtual IP. This virtual IP is given out to the world for email services. If the primary server goes down, vqalive automatically assigns the virtual IP to the backup server. When the failed machine comes back on line vqalive will automatically make it the secondary server, ready in case the primary server has a problem.
Typical email server configurations also incorporate a method for sharing the emails between servers with either a shared data store or syncing the secondary server with the primary.