One of my client has below requirement.
1) User send an email to client domain. Say mail address is email@example.com.
2) Client is using EOP. When mail hit EOP, I created a rule to forward, that mail to another domain (Client vendor domain). Example Domain name is: firstname.lastname@example.org
3) Once vendor receives that mail, vendor replies to that mail, as email@example.com. So, user can see that mail, as it is coming from xyz.com not from abc.com
4) As vendor is spoofing client address, mails are getting blocked or going to spam.
In short, requirement is to allow vendor to send mail as client.
If anyone performed, such task in their environment. I am open for all options. Even creating new domain for client. If more info needed, let me know.