i have a CENT OS 5.5 64 bit mail server.I want my main postfix mta to relay mails sent or received to multiple postfix instances, the other postfix instances will perform the mail sending and receiving work, i.e. i want to use multiple mta in a single mta because Multiple instances give the freedom to tune each Postfix instance to a single task that it does well and to combine instances into complete systems. . can anyone help me with this.
Look at http://www.postfix.org/MULTI_INSTANCE_README.html and http://www.postfix.org/postmulti.1.html. Also, http://eric.lubow.org/2010/mail/a-few-words-about-setting-up-postfix-multi-instance/ will give you a quick start, but don't expect it to be a substitute for the other two.
I'm not sure what the support for postmulti is like in Centos, but the support in the init.d script that comes with Debian wheezy's distribution is good, and I expect you could copy the relevant bits. (That script also works verbatim if transferred to Debian squeeze). The init script support is really all you need to integrate with the OS.