Mass E-mail Problem

I try to send e-mail by Mass E-mail of ACP

When I selected one person to mail , it is success.

But When I selected more than 2 person . It is failure .

And log is show

"Errno 2: mail(): SMTP server response: 553 5.1.3 <undisclosed-recipients:;>... List:; syntax illegal for recipient addresses at [ROOT]/includes/functions_messenger.php line 1843"

I checked about messenger.php line 1843, it is shown

"$result = mail($to, mail_encode($subject, ''), wordwrap(utf8_wordwrap($msg), 997, "\n", true), $headers, $additional_parameters);"

I had tried to re-install to another system.The probles is the same.