So you want the original email to be included in the auto reply, right? If this is the case, it's not feasible right now using the native features in either Exchange or Outlook.
From the perspective of Outlook client side, however, in theory you can follow the steps below:
- Add the shared mailbox as an account in Outlook (Authenticate using the credential of a user who have full access to the shared mailbox. Refer to this link for details. ).
- Refer to the link below to use Outlook VBA codes for your need: Outlook VBA codes
How to Auto Reply with the Original Email and a Predefined Text via Outlook VBA
But please be aware that, as indicated in the linked article above, this method can only make effects when the Outlook is running. So, seems to me that it's not practical as keeping the Outlook running all the time is not that realistic.
With the above being said, I'd recommend posting it to the official feedback portal as well to request this feature.
https://aka.ms/ExchangeServerFeedback