Transport Load Balancing

Hello,

I'm currently working on building a mail system with High
Availability and High Performance based on Postfix (at the MTA side). I
receive mails from internet to a VirtualIP that balances between a group
of MTA servers, taking off the group a server if it is not up && running.

This level has to deliver the mail to a group of backend server,
where the mail is stored. At this point I would not like to use a
LoadBalancing hardware, instead use load balancing based on a RoundRobin
algorithm at the transportation level of postfix. Something (at the
transport table) like:

domain.foo smtp:mbox1,mbox2,mbox3

Is that possible??

Thanks in advance

Agustin