When you send an email to multiple people, those people can see who else got that email. But if you don't want certain email addresses to be visible to others, this is how you do it in Outlook 2010 in secrecy.
If you need, besides major accounts, an extra account with limited access to data, you can add Windows 8 Guest account. The process is almost the same as in Windows 7.
You may have noticed that Facebook ads a the location revealing your wheresbouts at the times you publish post. If you don't want other to know that, this is what you need to do.
