This policy setting enables you to designate a required certificate authority for Outlook to use for encryption and digital ...

This policy setting enables you to designate a required certificate authority for Outlook to use for encryption and digital signatures.If you enable this policy setting, you can specify a required certificate authority by entering an X.509 distinguished name in the text field that is provided. The name must conform to the X.509 certificate format exactly. For example:CN=WoodgroveBankCA, DC=WoodgroveBank, DC=comIf you disable or do not configure this policy setting, Outlook trusts any certificate authorities that are represented by certificates in the Trusted Root Certification Authorities store on users' computers.