Outlook E mail Security

Is anyone out there having troubles with the administration of the Outlook security? We have an Exchange 5.5 installation and are using an Outlook Security Setting folder to allow the receipt of some level 1 attachments. For the most part it seemsthe allowed level 1 attachments are stripped off messages, although this behavior is not consistent through the company. On some workstations the things seem to work properly on others some of the attachments are blocked. Any ideas?