Hello,
As metioned in my last reply, if you have Full Access permissions on your delegate mailbox, we can do this via build-in Outlook account configuration options and settings:
Change default and delegate/shared mailbox
Configure an additional Exchange account
Please take a look at the link I provied in my last reply. It provided methods for this question not only via build-in Outlook account configuration options and settings but also provides a code sample to set the From address programmatically.
Best Regards,
Steve Fan
TechNet Community Support