I want a load balancer for outgoing mail.
My smtp mail server should generate mail and it must relay mail from other mail servers(Multiple relay host) .so how should i configure postfix to relay mail from multiple relay hosts..
plz help me with this
sorry for my bad english...

There is no way that I know of to tell Postfix to send X messages to one relay and then X to another for "load balancing". The only way that I can think of to do something like this is that you would have to configure the relay domain in DNS with multiple MX records and hope that it picks one some of the time and the other some of the time. What will probably happen is that Postfix will pick the higher priority one and being standards compliant will use that one exclusively.

I think you will need a different tool for the job. See: http://en.wikipedia.org/wiki/SMTP_proxy