Welcome to the thread, @TNTTinting.

Let me get the help you need to resolve the bounced email delivery errors so you can email invoices successfully. 

I've checked the investigation (INV-69467) regarding bounced emails and it was already closed. Since you're still getting the same error, let’s try performing some basic troubleshooting to fix the issue. 

The first thing to perform is to access your QuickBooks Online (QBO) account using an incognito browser. This is to isolate if a webpage issue is causing the problem.

Check out these keyboard shortcuts:

• Command + Shift + N (Safari)
• Ctrl+ Shift + N (Google Chrome)
• Ctrl + Shift + P (Mozilla Firefox) 

Once done, try to email an invoice again. If it works, go back to your default browser and clear the cache. See Clear cache and cookies to fix issues when using QuickBooks Online for more information.

Otherwise, switch to a different browser like Firefox, Google Chrome, or Safari. The one you are currently on maybe have a temporary issue with QuickBooks, and using a new browser for the moment will allow you to get back to work.

However, if the issue persists, I recommend contacting our Customer Care Team for further assistance. They have tools like screen-sharing that will help check the root cause and find a permanent solution to this problem. Then, as a workaround, you can send the invoice to your email and resend it to your customers.

To reach them, click the ? Help button at the top-right corner and select Contact Us to talk with a live agent. Ensure to review their support hours to know when agents are available.

To help you add, organize, and send invoices, see our Community link for reference: Invddoices and payments. It contains related articles on the process.

For your future task, check out this article to learn how to receive invoice payment in QuickBooks Online. 

Please keep me posted on how it goes from your end. I want to ensure you'll get past the error so you can email invoices to your customers.