This policy setting controls whether Outlook 2007 blocks potentially dangerous attachments designated Level 1. To protect users from viruses and other harmful files, Outlook 2007 uses two levels of security, designated Level 1 and Level 2, to restrict access to files attached to e-mail messages or other items. Potentially harmful files can be classified into these two levels by file type extension, with all other file types considered safe. See Attachment file types restricted by Office 2007 (http://r.office.microsoft.com/r/rlidGPOutlkAdminAndUserSet2?clid=en-us) for the full list of file types classified Level 1 by default.
If you enable this policy setting, Outlook 2007 users can gain access to Level 1 file type attachments by first saving the attachments to disk and then opening them, as with Level 2 attachments.
If you disable this policy setting, Level 1 attachments will not display under any circumstances.
If you do not configure this policy setting, Outlook completely blocks access to Level 1 files, and requires users to save Level 2 files to disk before opening them.
Important - For this policy setting to apply, you must also enable the "Outlook Security Mode" policy setting in User Configuration\Administrative Templates\Classic Administrative Templates (ADM)\Microsoft Office Outlook 2007\Security\Security Form Settings\Microsoft Office Outlook 2007 Security and select Use Outlook Security Group Policy from the drop-down list.