Hi @ Timo Schulte,
Based on my research and search, we can't set this setting to be selected by default in the EAC.
If you feel it is troublesome to configure forwarding in batches in the EAC, I recommend that you set forwarding through the DeliverToMailboxAndForward parameter with PowerShell:
Set-Mailbox -Identity "Douglas Kohn" -DeliverToMailboxAndForward $true -ForwardingSMTPAddress "******@fineartschool.net"
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