There isn’t a setting that I am aware of that can be used for this. Looking through my personal email inbox, it seems quite common for the From and Reply To fields to not match. I’m seeing examples of applications sending emails from a no-reply email address with the Reply To address set to the proper address for replies. Other applications seem to be handling it in the same way as Discourse is - with a real-looking From address, but with the expectation that the Reply To email address will be used for the reply.
Unless there is a site setting that I’m not aware of that lets you set the From address to noreply@<domain.com>, adding one seems like a reasonable feature request to me.
The email template that is being used by Discourse for these replies is the email_reject_bad_destination_address template. This email template is supposed to be listed in the site’s email templates section (found at Admin / Customize / Email.) When I search my site for that email template, I am not finding it. It looks to me like this is a bug that needs to be fixed. We need to add the template to the list found at discourse/app/controllers/admin/email_templates_controller.rb at main · discourse/discourse · GitHub. This is a small change, so we should be able to get it done very soon.
For now, you can edit the email_reject_bad_destination_address template by going to your site’s Admin / Customize / Text section and entering the following text into the search box:
system_messages.email_reject_bad_destination_address.text_body_template
Click the “edit” button that’s displayed next to the search result that is returned to make your changes.