如何仅使用电子邮件信息更改用户AD密码。 PHP

I'm working on a project to change user AD password by using a token. How can I find a user DN with only the user EMAIL?

In other words I have the user e-mail and I want to get the user DN.

$result = ldap_mod_replace($ds, $UserDN , $userdata);
$ds = connection to ldap "Already done"
$userdata = User new password"Already done" 
$UserDN = That's what I have the problem. 

Really thank you guys. :)

Problem solved!

Code:

$res = ldap_search($ds, $basedn, $filter);
  $first = ldap_first_entry($ds, $res);
  $data = ldap_get_dn($ds, $first);
  echo "The desired DN is: ".$data;
  $userdata['unicodePwd'] = iconv('UTF-8', 'UTF-16LE',"\"" . $password1 . "\"");
  $result = ldap_mod_replace($ds, $data , $userdata);