This is under Email Security > Change Security Settings in Outlook 2016. I have two certificates for email encryption and when I pick #2, it will not save the selection. I can click back and forth between #1 and #2, so it's registering my choice. But when I hit OK it does not save the certificate I chose. Both certificates are installed and imported successfully. This happens on both user accounts on this computer. I've already re-installed Outlook and very close to just re-imaging the computer.