This kind of issue will happens so many times. Typically, if the problem is on your end then you’ll get an email notifying you that the email was not delivered. Ask the recipient to check his or her junk folder to see if your email was marked as spam and thus not placed in his or her Inbox . Ask the recipient to add your email address to his or her whitelist.
The test emails go to 2 of my own test emails. Previously they worked and I’m not getting a notification saying they’ve failed and they aren’t in the junk folder. Can you think of anything else because phpList says they have gone successfully.