User Configuration > Administrative Templates > Microsoft Outlook 2016 > Security > Cryptography
User
HKCU\software\policies\microsoft\office\16.0\outlook\security
This policy setting controls whether Outlook users can publish e-mail certificates to the Global Address List (GAL). If you enable this policy setting, the "Publish to GAL" button does not display in the "E-mail Security" section of the Trust Center. If you disable or do not configure this policy setting, Outlook users can publish their e-mail certificates to the GAL through the "E-mail Security" section of the Trust Center.