Thanks for joining us here in the Community, @SoftwareTeacher.
To help verify why you're unable to send emails through the Microsoft Exchange Account, I recommend contacting the Customer Support Team. This way, they'll be able to check the account setup and determine the root cause of this issue, since you already tried some troubleshooting steps.
To add up here are some links that you can visit about connecting an email server and fixing its error in QuickBooks Desktop for reference:
I've got your back if there's anything else you need. I'll make sure you're all set. Have a good one!
