Emailed PDF not going into proper Sent Items folder

We send out invoices opened in Acrobat Reader DC, using the email icon, it opens Outlook (2013) and displays the new message with PDF attached as expected,  we change the From address to a shared mailbox and send successfully, but the message goes into the Sent Items of the current user's mailbox rather than the Sent Items folder of the From address's mailbox. (We are using hosted Exchange)

I though I had it solved with the following Send As registry setting:

HKEY_CURRENT_USER\Software\Microsoft\Office\x.0\Outlook\Preferences
Note The x.0 placeholder represents your version of Office (16.0 = Office 2016, 15.0 = Office 2013, 14.0 = Office 2010).
1.    On the Edit menu, point to New, and then click DWORD Value.
2.    Type DelegateSentItemsStyle, and then press Enter.
3.    Right-click DelegateSentItemsStyle, and then click Modify.
4.    In the Value data box, type 1, and then click OK.

While that works if you just launch Outlook and create/send a new message, it doesn't work if try it using the email icon within Adobe Reader.

Any assistance would be appreciated.

I know there are other ways to do in manually vs using the email icon in Adobe Reader, but end users are demanding that way

Thanks

Doug