I have an exchange server on my network. We have multiple domains mycompany1.com, secondcompany.org, etc.
I want to be able to accept and relay an email with a 'from' address from one of my domains without having to use authentication.
I don't want relay only based on IP.
Here's why: I have a public facing web based application that generates email notifications. The server was hacked and being used to relay spam. All the spam messages had a bogus 'from' - somewhere in france. If is used regular authentication, the web app would still authenticate and still send all the bogus spam messages. So, on the exchange side, if I only accept emails with 'from' using a valid domain that's part of my exchange server, that would minimize the problem.
How would I setup my exchange server (relay connector or transport rule?) to accept and relay messages with a from domain that exists on my server?