Thanks for joining this thread to let us know your concern, Sue0909. 

I'm here to help point you in the right direction for support with your concern about emailing invoices in QuickBooks Desktop (QBDT).

I appreciate you performing all the troubleshooting steps to resolve this. Since none of them work, I recommend reaching out to one of our Customer Care Team. This way, they'll be able to further investigate the main cause of the issue and provide steps to fix it.

You can follow the steps provided by my colleague @AbegailS on how to reach them. For more details, check out this article: Contact QuickBooks Desktop support. 

I've got you this article for more details: Troubleshoot PDF and Print problems with QuickBooks Desktop. This helps in fixing any printing, emailing, or saving PDF files.

Please let me know how it goes. I'll be right here to help you out with fixing emailing or printing invoices. Have a great day!