为什么 PhpMailer 在某些机器上失败

我正在使用PHPMailer发送电子邮件。我的问题是，从我的PC上一切正常，但是在其他设备上，例如其他人的笔记本电脑或PC会给出以下错误：

SMTP Error: Could not authenticate. Mailer Error: SMTP Error: Could not authenticate.The following From address failed: confidential@confidential.com Mailer Error: The following From address failed: confidential@confidential.com 

SMTP 服务器错误：未播发时使用 AUTH 命令

有人可以对此有所了解吗？！

我的代码：

$mail             = new PHPMailer(); // defaults to using php "mail()"
$body             = stripslashes($_POST['textarea']);
$body = str_replace(' ',' ',$body);
$body = str_replace('/media/','http://www.confidential.com/media/', $body);
$body = $body;
//$body             = eregi_replace("[']",'',$body);
    $mail->From       = "confidential@confidential.com";
    $mail->FromName   = "confidential confidential";
    $mail->CharSet  = 'UTF-8';
    $mail->Subject    = $_POST['subject'];
    //$mail->IsSMTP(); // telling the class to use SMTP
    //$mail->Host       = "confidential.com"; // SMTP server    
    //$mail->SMTPAuth   = false;                  // enable SMTP authentication 
    //$mail->Port       = 25;                    // set the SMTP port for the GMAIL server
    //$mail->Username   = "confidential@confidential.com"; // SMTP account username
    //$mail->Password   = "confidential";        // SMTP account password
    $mail->SetFrom('confidential@confidential.com', 'confidential confidential');
    $mail->AddReplyTo("confidential@confidential.com","confidential confidential");     
    //$mail->SMTPDebug = 1;

此外，当我使用SMTP身份验证时，每个设备上都有以下下一个错误：

SMTP Error: Could not authenticate. Mailer Error: SMTP Error: Could not authenticate.SMTP Error: The following recipients failed: someemail@test.com Mailer Error: SMTP Error: The following recipients failed: someemail@test.com

SMTP 服务器错误：身份验证失败

更新：

导致完全错误：

SMTP -> FROM SERVER:220-sclabo15.ds.systemsunit.com ESMTP Exim 4.86_1 #1 Wed, 16 Mar 2016 13:10:25 +0200 220-We do not authorize the use of this system to transport unsolicited, 220 and/or bulk e-mail.
SMTP -> FROM SERVER: 250-sclabo15.ds.systemsunit.com Hello confidential.com [176.223.213.66] 250-SIZE 52428800 250-8BITMIME 250-PIPELINING 250-AUTH PLAIN LOGIN 250-STARTTLS 250 HELP
SMTP -> ERROR: Password not accepted from server: 535 Incorrect authentication data
SMTP -> FROM SERVER:250 Reset OK
SMTP Error: Could not authenticate. Mailer Error: SMTP Error: Could not authenticate.SMTP -> FROM SERVER:250 OK
SMTP -> FROM SERVER:550 Authentication failed
SMTP -> ERROR: RCPT not accepted from server: 550 Authentication failed
SMTP Error: The following recipients failed: confidential@confidential.com Mailer Error: SMTP Error: The following recipients failed: confidential@confidential.com
SMTP server error: Authentication failed