The fields `to`, `cc` and `bcc` can contain a player, multiple player names separated by commas, or be empty.
Players in `to` are the recipiants, who are addressed directly. `cc` specifies players that get the mail to get notified, but are not immediate part of the conversation.
There is no technical difference between `to` and `cc`, it just implies meaning for the players.
Players can see all fields making up the mail except `bcc`, which is the only difference to `cc`.