Only subject of my emails are wrong

I'm having problems with subject of emails..

exemple of my subject:
Confirmação de inscrição na newsletter.

the body is OK.

my source of email.

.........
Subject: =?iso-8859-1?Q?Confirma=C3=A7=C3=A3o_de_inscri=C3=A7=C3=A3o_na_newsletter?=
=?iso-8859-1?Q?_da_Bauma.?=
Message-ID: <1139a2a8168297321160c9498d4bb5ea@www.bauma.net>
X-Priority: 3
X-Mailer: PHPMailer 5.0.0 (phpmailer.codeworxtech.com)
MIME-Version: 1.0
Content-Transfer-Encoding: 7bit
Content-Type: text/html; charset="iso-8859-1"

"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

......

Do you have any idea of how can I fix it??

myhook_mail_alter
......
$message['headers']['Content-Type'] = 'text/html; charset=UTF-8';
$message['headers']['Content-Transfer-Encoding'] = '7bit';
.........

Thanks