How to get the user id by an email address?

i have an email of a user.
How do i get a user id by the email address?

$user->retrieve_by_string_fields(array('email1' =>  $organizerEmail));
doesn't work.

looked it up , no answer, only how to get the current user email addess , which i dont need.

Using SugarCRM community 6.5.13