When I invoice I have it emailed to both user and a copy to me. On two of my accounts when I invoice them a email is not being sent out. The invoice is created. And when I change the override email address to my own address to test it then it works but when I use their own email address it doesn't work. It's not even going out or attempting to. Any ideas or where to look?
Yes, it shows the date, time, 1, and "NOT_DELIVERED" on all of these. I also noticed it has not worked on another account also.
That means it attempted delivery, but it was rejected by the SMTP server, so the next step would be to check the logs on the mail server to find out why it didn't accept it for delivery.