You need to design security for messages exchanged between Northwind Traders employees and its vendors. What should you do？（）

• A、Require employees to access e-mail only over connections that use SSL
• B、Place Exchange mailbox stores on NTFS volumes. Use Encrypting File System （EFS） to encrypt the stores
• C、Use the internal certification authority （CA） to issue certificates to all employees. Require employees to digitally sign outbound e-mail
• D、Use the internal certification authority （CA） to issue certificates to all employees and vendors. Instruct employees and vendors to use secure MIME to encrypt all e-mail sent between them