Are there any others out there having an issue with undelivered invoices?

Hello sharonleewilson,

In QuickBooks Online emails got undelivered or bounce due to the following:

• The email address entered was incorrect
• There was a temporary issue with the recipient's email server
• Display problem
   

To isolate the situation, please verify that the email address that you have for the customer is correct, edit if needed and try and send again. If you're getting the same result, you can try sending the transactions through your own email address and see if the invoice was sent and received.

If the undelivered status continues, I'd recommend reaching out to our Support Team, a representative can look into your account securely and add your name to the list of affected users. 

Also, you can check this article about invoices not sent 3 solutions for you when customers aren't receiving your emails.

Post again in the Community if you need more help with QuickBooks Online. Have a nice day!