Why do I recieve Bounced Email Delivery Errors for Invoices sent to valid Email addresses?

Hey there, chriso1. 

Thank you for posting here in the Community. When an email is sent to your clients from your QBO company, the email goes out from our server. If the email is bouncing, the recipient's email service sends a failure or delivery notification to your email service. If the delivery failure error is sent to us by your email service provider, a notification is added to the transaction stating the email delivery failed. Based off of your description of what's happening, it sounds like the recipient's email service is sending you the failure even though they're receiving the emails. You can find this info at the following link: How to view list of bounced emails with delivery errors. Just out of curiosity, the emails that are bouncing back to you, are they all coming from the same email provider? (Gmail, hotmail, aol, etc) or are they all different providers. 

This information will be able to help me come up with the best solution to your problem. Thank you and I look forward to hearing back from you.