In some cases you may want to send emails that are not logged in Salesforce. These may be personal emails, or business emails containing sensitive communication that should not be logged.
There are three ways to send an email without having it logged in salesforce.com.
For further privacy settings:
Here are options to send private emails:
And here is an option to make all Emails company-wide in Salesforce private:
And even further company-wide privacy settings: