What solutions are there for email addresses that are verified to be correct but quickbooks does not send invoice?

Fixing a problem with sending invoices would depend on the circumstances or the indicated error notification when initiating this action, Steve. I'll outline some troubleshooting procedures you can follow to handle this situation.
 

To accurately asses your concern, may I ask if you've encountered an error message while sending the invoice to your customer? Any further information could help us provide a precise resolution.
 

In the meantime, you can open your account and send your invoice through a private browser. This provides a secure browsing experience that prevents data from impacting your activities on the platform.

Follow these keyboard shortcut keys to proceed:

• Mozilla Firefox: Ctrl + Shift + P
• Microsoft Edge: Ctrl + Shift + N
• Google Chrome: Ctrl + Shift + N
• Safari: Command + Shift + N

If you can send the invoice seamlessly using the private session, revert to your regular browser and clear its cache and cookies. Doing so eliminates outdated data utilities that affect the platform's performance. You can also consider using another supported browser if the issue persists.

Furthermore, you can also check out this link, which consists of resolutions for handling situations like unreceived sales forms from QuickBooks: Troubleshoot if customers aren't receiving emails from QuickBooks Online.

I'm also sharing this article, which you can utilize once you want to personalize your sales forms according to your business preference: Customize invoices, estimates, and sales receipts in QuickBooks Online.

Finally, if you need help streamlining your accounting processes, our QuickBooks Live Expert Assisted can help you achieve this. We have dedicated bookkeepers who can ensure your books are handled precisely on the platform.
 

Please keep us posted about the error notification you've encountered when sending your invoices by replying to this thread. Rest assured that we'll get back to assist you accordingly.