Hi,
In outlook, when you write a new email, Options > From
Then you choose the other mailbox in the from field, and enter the shared mailbox there
In OWA, choose show from then enter the shard mailbox
If an Answer is helpful, please click "Accept Answer" and upvote it.
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.