Hi @ Uwe Prohl
Welcome to our forum!
Based on my research, it is not supported to send emails directly from Shared Mailbox Account without using the ‘From’.
Please kindly understand that many functions are not designed at present. To get this feature more quickly, I have found a post in feedback collection website and you could vote for it. Many features of our current products are designed and upgraded based on customers’ feedback. You can also make suggestions on that website and hope Microsoft will notice this in the future.
Thanks for your understanding and support!
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