A、Configure and publish a certificate template that is suitable for S/MIME, Deploy a Group Policy object （GPO） so that a certificate that is based on this template is automatically issued to all domain users

B、Specify Group Policy objects （GPOs） and IPSec policies that require all client computers to use Kerberos authentication to connect to mail servers

C、For each mail server， acquire an SSL server certificate from a commercial CA whose root certificate is already trusted

D、Require IPSec encryption on all TCP connections that are used to send or receive e-mail messages