Question about multiple postfix instance, very strange

[coofucoo]

I want to set up a postfix mail server which have many IP. Each of
the
ip will work for one of my customer. So that is means my customer
will
think that he has a dedicate mail server. But in fact all the mail
server are running on one real machine. I think I can use the
multiple
instance feature to implement this requirement. So I setup 2
instance
for test. After that I find instance A(default instance) works good,
but instance B looks very strange.

First, smtp_dns_lookup not work. I set this parameter to "native" to
make sure postfix can use /etc/hosts file first. But for instance B,
it will use dns lookup first.

Second, the mydestination not work.

For instance, the mail ro...@mailcent211.coofucoo.com, if I sent it
to
instance A, it will be received. But if i send to instance B, it
will
not receive it, but start to lookup dns.

It is very strange, it is long time that I can not find any
solution.
Does postfix support the way that I wish to do?

Who can fix this problem? Thank you very very much!