Reference: Address a Mail Message
This is the list of recipients from the address book that will receive the message. There are three categories: Direct recipients; Copied recipients; and Blind copy recipients. The latter category receives the message without knowledge of other addressees. Addresses are Added to these lists using the To:, Cc:, or Bcc: buttons. Entries may be deleted by double-clicking, or by selecting the appropriate entry and pressing the Delete or Del keys.
Note: Selections are made with the left mouse button. Multiple selections are supported when the Shift and Ctrl keys are combined with the mouse button.
Warning: Do not use the Remove button to delete members of a recipient list. This will remove the selected address book entry!