Looking for help on a Back up server for mail

I am not really sure the technical name but I would like to build another WebMail server and have it serve as sort of a Back Up mail server so if the main server went down I would still have ALL of the emails that were sent to the main WebMail Server.

Any help would be greatly appreciated.

 

Keep the mailboxes in sync between both servers with unision, drbd,glusterfs, rsync...

 

Thanks.

Sometimes it is right in your face and you just can not step away long enough to look at it a different way.

Thanks again. "
"Genius"