Replies or forwards to signed/encrypted messages must be signed/encrypted.

This policy setting controls whether replies and forwards to signed/encrypted mail should also be signed/encrypted. If you enable this policy setting, signing/encryption will be turned on when replying/forwarding a signed or encrypted message, even if the user is not configured for SMIME. If you disable or do not configure this policy setting, signing/encryption is not enforced.

Verify the policy value for User Configuration -> Administrative Templates -> Microsoft Outlook 2016 -> Security -> Cryptography "Replies or forwards to signed/encrypted messages are signed/encrypted" is set to "Enabled".

Procedure: Use the Windows Registry Editor to navigate to the following key:

HKCU\Software\Policies\Microsoft\Office\16.0\outlook\security

Criteria: If the value NoCheckOnSessionSecurity is REG_DWORD = 1, this is not a finding.

Set the policy value for User Configuration -> Administrative Templates -> Microsoft Outlook 2016 -> Security -> Cryptography "Replies or forwards to signed/encrypted messages are signed/encrypted" to "Enabled".