stop emails from shared mailbox saving in users sent items

[mishaqit]

how i can stop sent item from shared mailbox saving on the user ( Primary ) email 

from Admin center - shared mailbox , we just allow ( Copied to mailbox )

[#2]

I don't believe you can, there will always be a copy in the sent items for the user sending the message. From my understanding the only control you have is whether the item also appears in the Sent items of the Shared Mailbox.
https://techcommunity.microsoft.com/t5/exchange-team-blog/want-more-control-over-sent-items-when-usi...