Site configuration for email

I want to set up active mail for each lms domain. How do I setup in site configuration ?
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https://edx.readthedocs.io/projects/edx-installing-configuring-and-running/en/open-release-koa.master/configuration/sites/configure_site.html

@Cover_Kami, the email_from_address setting controls the from address of the emails sent out from a site and I can see that you have already configured it. So can you explain in more detail about what exactly you are trying to achieve here?