Can only email some invoices

Hello there, Sandra. I've got some information about undeliverable invoices in QuickBooks Online. 

Currently, we have an ongoing investigation into undeliverable or bounced email errors for invoices in the program. Rest assured that our product engineers are already informed about this issue and working actively to have a permanent fix as soon as possible. Thus, I recommend contacting our Customer Support team, so you'll be added to the list of affected users. This way, you'll receive an email update about the investigation and be notified once a resolution is available. You can follow the steps below to reach us:

1. Sign in to your QuickBooks Online account.
2. Go to Help (?), then select the Search tab.
3. Click Contact Us.
4. Select the topic to connect with the right expert or choose Ask about something else and provide a brief discussion of your concern.
5. Click Continue.
6. Choose a way to connect with us:

• Start a chat with a support expert.
• Get a callback from the next available expert.

In the meantime, you can download the invoices in a PDF file, and manually send it to your customer through your personal or company email as a workaround. 

Also, once you receive the payments from your customers, you can record it in QuickBooks to link it to the existing invoice in the program and mark it as paid. 

You can always count on us if you have other questions and concerns about managing your invoices and other QuickBooks-related queries. We're here to help you address them. Have a great day!