Add a new mime types for the files. You need to use this with addtional hook if you adding new types of extensions https://www.opensource-socialnetwork.org/documentation/view/5560/file-allowed-extensions

~~~
<?php
function my_component_init(){
ossn_add_hook('file', 'mimetypes', 'my_component_hook');
}
function my_component_hook($hook, $type, $types){
$types['rar'][] = 'application/x-rar-compressed';
return $types;
}
ossn_register_callback('ossn', 'init', 'my_component_init');
~~~