If you takeintoaccount cost, you can choose create an internal relay domain in source organization.
If you have moved the recipient to target organization and delete the recipient from source domain, after you configure an accepted domain that's as an internal relay domain first tries to deliver to the recipient in the Exchange organization. If the
recipient isn't found, the message is routed to the Send connector that has the closest address space match.
Please refer to the "internal relay domain" section in the following article.
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