Does not show the body of the email when I use the wp_mail function of Wordpress

I'm using the wordpress wp-mail function in the code below, but the body content of the email arrives as a noname.txt attachment file.

$body .= "<h2>Dados do Cliente</h2>

<strong>Nome:</strong> " . $user_info->first_name . " " . $user_info->last_name . "<br>
<strong>Especialidade do Médico:</strong> " . get_usermeta($user_id, 'especialidade_medico', false);

$body .= "</p>";
$mail_attachment = array();


$headers = "Content-Type: text/html; charset=UTF-8";
wp_mail($to, $subject, $body, $headers, $mail_attachment );