Launching Email from 3rd party app with Outlook 2016

We use a software product called Formdocs that does electronic forms for us.    In the past with Windows 7 and Outlook 2007 we could program an electronic form to launch an Outlook email and prefill the recipient(s).   With Windows 10 and Outlook 2016 this feature does not work.   We can launch a new email without pre-filling recipients, and that works fine.   It’s only when the software does the prefill.    Does anyone at RTM have any ideas on what might be the cause?    We tried uninstalling Trend Anti-virus and using Microsoft defender in thinking it might be the anti-virus but that didn’t help.
The runtime error we get from Formdocs is really unhelpful, and their support department just tells us the issue is with Windows or Outlook.   Not them.   They have never been very good support-wise.