How to change dropdown field function to buttons in privatemsg module
You can implement hook_privatemsg_thread_operations_alter(&amp;$operations) (unfortunately not documented but called in _privatemsg_action_form()) to change the mark as read and mark as unread operations to use a button, as does delete. They are defined in privatemsg_privatemsg_thread_operations().

Something like this:

&lt;?php
function yourmodule_privatemsg_thread_operations_alter(&amp;$operations) {
  $operations['mark as read']['button'] = TRUE;
  $operations['mark as unread']['button'] = TRUE;
}
?&gt;


Note: This requires Privatemsg 6.x-2.x