The form submits. The green message appears. The email never arrives. Before you start disabling plugins, understand what that green message actually certifies — because the answer explains the entire problem, and it comes from CF7's own documentation.
What the green border actually means
Contact Form 7 sends mail through WordPress's wp_mail() function. The green success message means exactly one thing: that function returned true. WordPress core is unusually candid about what that is worth:
"A true return value does not automatically mean that the user received the email successfully. It just only means that the method used was able to process the request without any errors."WordPress developer reference, wp_mail()
And CF7's own FAQ, answering "I see a green border response but I never receive a mail", is even more direct:
