1. about mail transport - I think it is easy but what with users - if postfix dont find user in local or virtual table, he (postfix) reject this message. this is postfix documentation about this problem: http://www.postfix.org/docs.html and title MS Exchange Integration
It works as designed, isn't it?
Or maybe i didn't fully understood what your question is.
2. it is possible to transport only selected users?? or only all domain?
Per-user transport is available too.
- For OpenLDAP backend, change value of attribute 'mtaTransport' of user object.
- For MySQL backend, change value of column 'transport' in table 'vmail.mailbox' to transport name.
You can manage per-user transport with iRedAdmin-Pro too, screenshot attached.
3. in exchange server is somthing like SMART HOST - you can send e-mail from exchange Server via Postfix. in this case, if domain are transport to exchange, as who I should authorized on the iRedMail server - or only add exchange IP to Postfix (main.cf) mynetworks??
I don't understand your question, sorry.