PHP LDAP 身份验证失败

我正在尝试使用PHP LDAP验证电子邮件ID和密码。只是我想进行身份验证，无需访问联系人、邮件或日历。只需要确认他是有效用户。主机名正确。端口号也正确。请帮忙。请注意我的场景

1. 我的邮件 ID 是 xxxxx@childcompany.com，用户名是 yyyyyy

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

   $username = 'yyyyyy@parentcompany.com'; //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 = 'xxxxx@childcompany.com' //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...";
    }
   

   }