Hello,
The thing is that the Email is valid but the SMTP rejects the Email. This should have successfully shown an Error Message. However, please find the following code in the include/sendemail.php File:
echo '{ "alert": "error", "message": "Email **could not** be sent due to some Unexpected Error. Please Try Again later.
**Reason:**
' . $mail->ErrorInfo . '" }';
and replace it with:
echo '{ "alert": "error", "message": "Email **could not** be sent due to some Unexpected Error. Please Try Again later." }';
This will not show the exact issue. However, it will show an Error.
Let us know if we can help you with anything else or if you find any further issues.