if (!filter_var($email, FILTER_VALIDATE_EMAIL)) echo json_encode(['valid' => false, 'message' => 'Invalid email format']); exit;

if (empty($email)) $error = 'Email is required'; elseif (!filter_var($email, FILTER_VALIDATE_EMAIL)) $error = 'Please enter a valid email address'; elseif (!checkdnsrr(substr(strrchr($email, "@"), 1), 'MX')) $error = 'Email domain does not exist'; else $success = 'Valid email address!';

// Usage $email = "user@example.com"; if (isValidEmail($email)) echo "Valid email address!"; else echo "Invalid email address!";