As per API specification, receiver will represent the list of receivers of the communication, but does not provide a explicit way to represent a cc or bcc repcipient for an email.
How can we distinguish the different types of recipients in a communication message?
This is a very good question, José.
My immediate feeling is that a communication management message (irrespective of the sending method - SMS, email, etc.) is always delivered to recipients individually. In other words, a given recipient is not aware of other recipients. BCC if you like.
Would be interesting to hear other opinions on this issue.
Hope it helps