Solution:

$msg_email = 'Email enviado com sucesso!';
header('Location: ../login.php?msg_email=' . $msg_email);
$mail->send();

Error - Cannot modify header information - headers already sent by ... :
$mail->send();
$msg_email = 'Email enviado com sucesso!';
header('Location: ../login.php?msg_email=' . $msg_email);