Some invoices emailed to customers are being bounced back even though they are the same email addresses. Is there an issue at the moment?

Emailing your customer's invoice is one way to let them know how much they owe you, @car-air. Having trouble performing this task can delay a part of your working progress. But don't worry, you've got the right person to help.

Let me go over and discuss some information about sending email issue in QuickBooks Online (QBO). 

To answer your question, yes, currently, there's an issue with some email providers blocking emails sent out of QBO. Our product engineers are aware of this and work deliberately to create a solution. Please know that resolving this is our top priority, and it will remain so until it is entirely fixed. 

In the meantime, you can save your customer's invoice as a PDF and send it via email using your business or other email address as a workaround. I'll guide you on how:

1. In your QBO account, navigate to the Sales menu and click Invoices.
2. Next, look for the customer's invoice and the dropdown arrow under the Action column. 
3. Select Print and click the Download icon. 
4. Follow the on-screen steps to save the PDF file.

Another solution is to send your customer a link to their invoice or estimate via SMS. Just select the Save and share link option on the form and click Copy link. After that, paste it into your SMS or messenger service.

On the other hand, you can also use the Send with Gmail feature (available only if you have a Gmail or G-suite email account) to send QBO forms from your address. 

For additional reference, feel free to check this article: 3 solutions for you when customers aren't receiving your emails.

Following the above steps will ensure you'll be able to send your customer's invoice. 

I'd be glad to offer further assistance if you have follow-up questions about the workarounds I've outlined. Please don't hesitate to post a reply below. I'm always ready and willing to lend you a hand. Take care.