Receiving form submission but user not receiving email to confirm email address

Hi there,

As the developer I am receiving the form submission email

eg:
You've had a form submission on from FirstnameLastname <[email protected]>. We are waiting for them to confirm their email address.

But the user is not receiving an email telling them to click to confirm email address. (Testing with a different email address with gmail.) Not in spam, waiting 5 mins, no dice.

Thanks,
J