Does anyone know why QB cannot deliver invoices to email addresses that are have been verified as correct?

It's nice to see you posting your concern here in QuickBooks Community, @paul-tomocgroup-.

I've checked with our resources and found out that there's an ongoing investigation about Invoices showing as undelivered in QuickBooks Online. Right now, our engineers are taking action to resolve the issue.

While we are working to fix this matter, we have a workaround that you can perform to ensure that you can send invoices to your customers. You can use the option to manually download the invoices and send them from outside of QuickBooks.

I also suggest to contact us so we can send you updates about the status of this case. 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: Invoices and payments. It contains related articles on the process.

For your future task, check out this article to learn how to receive invoice payments in QBO. 

Thanks for your patience. If you need further assistance when working with QuickBooks, just let me know. We are always here to help you.

@paul-tomocgroup- 

For your reference

https:// quickbooks.intuit.com/learn-support/en-us/other-questions/intuit-ips-found-in-spamcop-blocking-list-preventing-vendors/00/1066289