I'm here to help you resolve this email-sending issue in QuickBooks Desktop (QBDT). JT317. 

This issue has to do with email addresses. We can perform some troubleshooting steps to resolve this problem. You can update your QuickBooks Desktop (QBDT) to the latest release. This way, you'll have the latest features and fixes. Then, check email settings to ensure they are configured correctly. 

Here's how to update to the latest release:

1. Navigate to the Update to the Latest Release page.
2. Ensure your product is selected. If not, click on the Change link and choose your QuickBooks product.
3. Click the Update button to download the update file.
4. Select Setup Automatic Updates to learn how to set QuickBooks to automatically download and install the latest updates.

To check the webmail settings:

1. Access the Preferences by going to the Edit menu. 
2. Select Send Forms from the left pane.
3. Under My Preferences, click the email account you are using, then select Edit.
4. In the Edit Email Info screen, go to the SMTP Server Details section and set the server name and port to your email provider settings. Refer to Set up your email service in QuickBooks Desktop for a list of SMTP servers and Ports.

You can visit this article for more detailed steps: Fix Error: Could not connect to the email server.

Moreover, here's an article outlining the steps to see the list of bounced emails with delivery errors: How to view a list of bounced emails with delivery errors.

Don't hesitate to comment below if you have further concerns regarding the email issue. I'll be sure to get back to you.