Hi @Glenn Maxwell ,
In a Microsoft 365 hybrid environment, when a user sends an email on behalf of another user, the sent email is saved in the Sent Items folder of the mailbox of the user who sent the email, not the mailbox of the user on whose behalf the email was sent.
However, these parameters are used to enable message copy for journaling purposes, not to change the behavior of how sent emails are saved in the mailbox.
If you want to automatically forward the sent email to the mailbox of the user on whose behalf the email was sent, you can create a transport rule to redirect the message.
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