Hi Cory,
As Kevin mentioned above, this is, unfortunately, a known issue in SmarterMail 15.x. However, it has been resolved in SmarterMail 16.3.6543:
Changed: SMTP and Delivery processes now utilize the From address in email headers if it is provided; provides better spoofing protection.
I'm afraid we aren't able to implement this change in SmarterMail 15.x as the foundation of the product doesn't support this change.
Andrea Free
SmarterTools Inc.
877-357-6278
www.smartertools.com