Email encryption in Exchange Server 2007

Dear Support Team,

Now, current environment is Exchange Server 2007 and Outlook 2007. We have some question.

1. How do I scan external/public domain before email sent out? Should I config in Exchange and Outlook 2007?

2. How do I encrypted email? Do you suggested solution? required 3rd party? Exchange or outlook?

3. Can I encrypted email only email that send to external email?

Thank you.