$mailer->AddAddress("aa@gmail.com");

$mailer->AddAddress("aaa@gmail.com, bbbb@gmail.com");
$mailer->AddAddress("'aaa@gmail.com', 'bbbb@gmail.com'");
$mailer->AddAddress(""aaa@gmail.com", "bbbb@gmail.com"");

$mailer->AddAddress("aaa@gmail.com");
$mailer->AddAddress("bbbb@gmail.com");

<?php

Yii::import('application.extensions.PHPMailer_v5.1.*');

class Mailer {

    private $mail;

    public function initialise() {
        try {
            require Yii::getPathOfAlias('application.extensions') . '/PHPMailer_v5.1/class.phpmailer.php';
            $this->mail = new PHPMailer(TRUE);
            $this->mail->IsSMTP();                           // tell the class to use SMTP
            $this->mail->SMTPDebug = 0;
            $this->mail->SMTPAuth = true;                  // enable SMTP authentication
            $this->mail->Port = 25;                    // set the SMTP server port
            $this->mail->Host = "smtp.test.net"; // SMTP server
            $this->mail->Username = "test.com";      // SMTP server username
            $this->mail->Password = "test";            // SMTP server password
            $this->mail->Mailer = "smtp";
            $this->mail->From = 'info@test.com';
            $this->mail->FromName = 'test@net.com';
        } catch (Exception $e) {
            echo $e->getTraceAsString();
        }
    }

    public function email($message, $sendTo, $subject) {
        try {
            $this->mail->AddAddress($sendTo);
            $this->mail->Subject = $subject;
            $body = $message;
            $this->mail->MsgHTML($body);
            $this->mail->IsHTML(true); // send as HTML
            $this->mail->Send();
            $this->mail->ClearAllRecipients();
        } catch (Exception $e) {
            echo $e->getTraceAsString();
        }
    }

}

?>