How to set up two mail domains within one mail system?

Question

Mail server

Tell me where to dig.
There is a live mail system postfix - exchange.
You need to set up sending emails from two different domains. One is now in use by the second new domain.

Answer 1

If I understand the scheme correctly:
Postfix is ​​a nurse, Exchange is a corp. mailer.
In Exchange, you can have as many Accepted Domains as resources allow. But one user can have only one PrimarySMTPAddress. And sending on behalf of another domain is problematic.
There is a crooked scheme for each user in the first domain - to start a rummaged box with his name, with some prefix, give this box a PrimarySMTPAddress of the second domain, and send mail from this rummaged box. Yes, it's not convenient, but without a 3rd party app (which I don't even know if they exist) - it's impossible to do this.
Or write your own addon for Outlook - where the user will choose the name of the domain from which to send (he will write something to the header), and write a transport agent for Exchange that will catch this header and send mail from the desired domain - changing Envelop headers.