phpmail在windows测试可以，下传到ubuntu就不灵了。为什么

phpmail在windows测试可以，上传到ubuntu就不灵了。为什么啊

function
postmail($receiver,$receiver_name,$subject_name,$smassage){

require_once("lib/class.phpmailer.php");
//include("lib/class.smtp.php");



$mail=new PHPMailer();



$mail->CharSet ="UTF-8";//设定邮件编码，默认ISO-8859-1，如果发中文此项必须设置，否则乱码


$mail->IsSMTP(); // telling the class to use SMTP
$mail->SMTPDebug = 1; // enables SMTP debug information (for testing)
$mail->SMTPAuth = true; // SMTP authentication
$mail->Host = "smtpcom.263xmail.com"; // SMTP server
$mail->Port = 25; // SMTP port

$mail->Username = "xx@xx.com"; // SMTP 账户名
$mail->Password = "xxx"; // SMTP 账户密码
$mail->SetFrom('xx@xx.com', 'web');
$mail->Subject = "$subject_name";
$smassage=str_replace('',' ',$smassage);
$smassage=nl2br($smassage);

$mail->MsgHTML("$smassage");
$mail->AddAddress("$receiver","t");

//echo "test: " ;




if(!$mail->Send()) {
echo "Mailer Error: " . $mail->ErrorInfo;
exit;
} else {
echo "Message sent!";
}
return true;
}
?>
------解决方案--------------------
linux下需要sendmail或者postfix支持
可查看一下/var/log/maillog日志查看一下具体的错误信息．