Hi RAL2,

Sorry for the late reply, buried under projects. I saw the MS thread, thanks for posting that.

The thought behind my previous fix was just this: Outlook uses a default template to send emails. When selecting the Outlook option to mail in QB, QB hands over the emailing process to Outlook/Windows. So I started looking into Outlook templates.
Maybe try this,

• Create a Windows 10 virtual machine, using any virtualisation software (vmware, oracle, azure, aws, free-paid anything)
• Install and configure office with the latest patches (dont configure Outlook)
• Install and configure QB (these steps are to mirror your affected user's setup).
• Install processexplorer (from Microsoft) or similar
• shutdown and take a snapshot of the vm, so you can keep rolling back as needed.

For the troubleshooting part,

+Open process explorer
+ Open quickbooks and a blank email in quickbooks

+ Check processexplorer for all the subprocesses and threads under QB.

+ It might take some googling but you should be able to find the registry entries and file locations for the different subprocesses.

My thought here is that, this should give you a rough visual of how QB is interacting Windows, Office through the steps above, which might help you figuring out the fix.

Also if you setup the vm, you can also try different fixes without having to re-setup the scenario every time.

I understand this is not much help, sorry :( but I am hoping it will help you troubleshoot further.

If I can figure out a solution, I will definitely post it.

Have a great weekend. :)