outgoing mail address change

Hi,

We have a standalone SME sever servicing the local domain foo_1.com

Our corporate mail is domain foo_corp.com

How can I set up the SME server to do the following:

1.When an internal(foo_1.com) user send mail to anyone
outside, all addresses containing foo_1.com should be
replaced with addresses in a map file:

   example:
   Mail to: internet@yahoo.com
   cc:    john@foo_1.com
   reply-to: user1@foo_1.com

      should be changed to
   Mail to: internet@yahoo.com
   cc:    john.smith@foo_corp.com
   reply-to: user1.surname@foo_corp.com

2.    The mails should still be delivered locally if the
address is local, it should not go out to the
corporate mail server and then back again to the SME
server.
Only the outgoing mail header should be changed.

Thanks in advance, rgds braam