This policy setting controls whether Outlook blocks potentially dangerous attachments designated Level 1. To protect users from viruses and other harmful files, Outlook 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 2010 (http://officeredir.microsoft.com/r/rlidGPOutlkAdminAndUserSet2O14?clid=1033) for the full list of file types classified Level 1 by default.
If you enable this policy setting, Outlook 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: This policy setting only applies if the "Outlook Security Mode" policy setting under "Microsoft Outlook 2010\Security\Security Form Settings" is configured to "Use Outlook Security Group Policy."