High Availability Email

[Gary C. New]

I am gearing up to migrate our systems to a high availability email 
topology and was wondering what the current solutions are to provide 
such an architecture?

I need a solution that synchronizes/mirrors/replicates user mail stores 
across several physical servers for redundency.

Some of my research has pointed me to Cyrus Murder and the MUPDATE 
protocol, but it sounds like even in this type of configuration the 
back-end server would still be a single point of failure.

Suggestions?

Thanks.

Gary