This week we’ve had 3 separate incidents where clients no longer receive notifications when their forms are submitted. Oddly enough the fix has been changing the sender from noreply@thedomain to [admin_email]. We haven’t made any changes to the websites or the server recently.
There are a number of things that can go wrong with the notifications. You can start troubleshooting with the information here:
However, I recommend submitted a support ticket here to get more personalized assistance.