Hi,
I've posted a few articles on your other thread. however what you need to do is set up a second outgoing and deployment profile to send out emails to a different smtp; on the deployment profile use one account that resides on the subcompany business unit
and make sure this account has only permissions at the business unit level.
The articles I posted on the other thread should help understand more about email router, however they don't cover this specific scenario.
Hope this helps.
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