Recipients

To – You need to have at least one recipient in the email. If you have selected a Contact, Lead, or Opportunity, this field will automatically be populated with the email address of that contact. It will not automatically be filled when you have an account or a case selected. The search buttons to the right of all three address boxes give you access to all of your Salesforce contacts.
Cc – Carbon Copy Recipients: enter email address(es) as a CC. All To and CC Recipients will be visible to everyone who sees the email, or you may leave this field empty.
Bcc – Blind Carbon Copy Recipients: enter email address(es) as a BCC. All To and CC Recipients will be visible to all the recipients, while any BCC recipients will not be displayed. You may add your own email address here if you would like to get a copy of the Thru Email, or you may leave this field empty.