It is an ongoing nightmare.  I have been having this issue since March of this year.  I thought it was resolved but now when I email invoices to anyone with a business email address or a gmail address, the emails are not delivered and I do not received a "bounced email" delivery notification.  It's a great waste of my time at year-end, open enrollment, "audit season" and budgeting!  I have posted so much about this issue I have just earned a new rank in the QB community so there's that.....