[exim] Per domain routing in Exim

Hello all.

I have a task to make a some hard mail system

Here is a scheme:

3 pop3\imap & SMTP servers. Each work with a number of domains. All
clients send email to it. Lest call it "newmail".

3-6 SMTP relays in 3 round robin group. They a MX for some number of
domains. Each group work with different domains. Lets call it MXs.

All mail from outside world send to MXs and they relay it to newmail.
All mail send by our clients sends to newmail - and it relay it to MXs.

I have few questions:

1) How make a router on newmail which will check domain part of SENDER
and send it to special MX.

For example. If I wrote email from my email@??? - send this mail
to mx.domain.com. If from email@??? senf it to mx.domain.org.

2) Same thing on MXs. If email RCPT TO domain part is *.com - send it to
newmail.com if to *.org - send it to newmail.org

3) Then client send mail from one of newmails it relay it to mx, mx send
it to recipient. I need to delete header "revived by newmail" then
message arrives to MX. For all world it must be looks like it send from
one of MX.

YES I know it is no good. But it is my task.

--
Best regards,
Proskurin Kirill