PHP LDAP认证失败

我正在尝试使用PHP LDAP验证电子邮件ID和密码。我只是想进行身份验证而无需访问联系人，邮件或日历。只需确认他是有效用户即可。主机名正确。端口号也正确。请帮忙。请注意我的情况

1. 我的邮件ID是[email protected]，用户名是yyyyyy

2. 我的邮件由母公司（mail.parentcompany.com）托管和处理

   $username = '[email protected]'; //If i use this line Unable to bind to server: Strong(er) authentication required 
   $username = 'yyyyyy';//If i use this line Unable to bind to server: Invalid credentials
   $username = '[email protected]' //If i use this line Unable to bind to server: Invalid credentials
   $password = 'mypassword';
   $ldap = ldap_connect("10.1.1.1",389)   ;  
   if ($ldap) 
   {   
      $ldapbind = ldap_bind($ldap,$username,$password );     
     if ($ldapbind) {
       echo "LDAP bind successful...";
    } else {
       echo "LDAP bind failed...";
    }
   

   }