Thanks for getting back to me User since 2008, we appreciate your longstanding support of QuickBooks and sincerely apologise for the disruption that this issue is continuing to cause to yourself and your business. Currently, our investigation has found that emails are being successfully sent from QuickBooks, but are being blocked by the customer's provider or by an external server. At the moment, we're implementing measures to fix this; if you haven't already, you can reach our support team here to be added to this so that you receive all email updates. We agree that an in-product notification would be valuable and we will feed this back to our team. In the meantime, please use the workaround provided to download the invoices and send these from outside of QuickBooks using read receipt. If you experience any difficulties using this workaround, please don't hesitate to reach out.