Information
This policy setting controls whether Outlook users can demote attachments to Level 2 by using a registry key, which will allow them to save files to disk and open them from that location. Outlook uses two levels of security to restrict access to files attached to e-mail messages or other items. Files with specific extensions can be categorized as Level 1 (users cannot view the file) or Level 2 (users can open the file after saving it to disk). Users can freely open files of types that are not categorized as Level 1 or Level 2.
Note: If this policy is enabled, users can create a list of Level 1 file types to demote to Level 2 by adding the file types to the following registry key:
HKEY_CURRENT_USER\Software\\Microsoft\Office\16.0\Outlook\Security\Level1Remove
The recommended state for this setting is: Disabled.
Rationale:
If users can demote Level 1 files to Level 2, they will be able to access potentially dangerous files after saving them to disk, which could allow malicious code to infect their system or compromise the security of sensitive information.
Impact:
Users will not be able to demote a Level 1 file to a Level 2 file.
Solution
To establish the recommended configuration via GP, set the following UI path to Disabled:
User Configuration\Administrative Templates\Microsoft Outlook 2016\Security\Security Form Settings\Attachment Security\Allow users to demote attachments to Level 2
Default Value:
Disabled. (Users cannot demote level 1 attachments to level 2.)