Loop Sending Emails with PHP

Question

Guys this is my first post and I would love your help: I have a query in a database that sends automatic email through PHP Mailer if the activity is delayed, so far so good, the problem is in repetition, if you have 3 emails to send is sent to the first ok, then the second receives ok (but the first email tb receives data from the second that was not to receive) and finally the first email receives the data from the third activity (which was not to receive). Could someone give me a light? Follow the code:

require 'conexao.php';

date_default_timezone_set('America/Sao_Paulo');
$hoje = date('Y-m-d H:i');

$conexao = conexao::getInstance();
$sql = 'SELECT ASSUNTO, PRAZO, RESPONSAVEL_GERAL, EMAIL_RESPONSAVEL FROM agenda WHERE PRAZO < :data';
$stm = $conexao->prepare($sql);
$stm->bindValue(':data', $hoje);
$stm->execute();
$clientes = $stm->fetchAll(PDO::FETCH_OBJ);

    require_once("class/class.phpmailer.php");

    $mail = new PHPMailer(true);

    $mail->IsSMTP();




try {
     $mail->Host = 'smtp.meuhost.com.br'; 
     $mail->SMTPAuth   = true;  
     $mail->Port       = 587; 
     $mail->Username = '[email protected]';
     $mail->Password = 'minha_senha';

     $mail->SetFrom('[email protected]', 'Agenda OnLine'); 
     $mail->Subject = 'Lembrete de Atividades em Atraso';


        foreach($clientes as $cliente):

       // Aqui pego o email do BD
        $mail->AddAddress($cliente->EMAIL_RESPONSAVEL;, 'Teste de Atividades em Atraso');
         // E aqui pego o assunto
             $mail->MsgHTML($cliente->ASSUNTO); 

             $mail->Send();
             echo "Mensagem enviada com sucesso para '.$cliente->EMAIL_RESPONSAVEL'.</p>\n";

             $email = '';

        sleep(10);

        endforeach;


    }catch (phpmailerException $e) {
      echo $e->errorMessage();
}


?>