if QA_FINAL_EXTERNAL_USERS is set, it is WP integrated.
In that case, you have to to a db query to select all users from the wp_users table, then run the query:
$users = qa_db_query_sub('SELECT user_email FROM wp_users');
while ( ($email=qa_db_read_one_value($users,true)) !== null )
$this->myImportFunction($email);
(See the complete version edited above)