In Release 2 and later, messages can be assigned a Priority, Private, and/or Return Receipt category. New Priority messages are heard first when listening to new messages. Private messages can not be forwarded. Return Receipt messages notify the sender when the message is listened to by the recipient. One, two, or all three categories can be assigned to a message.
In a Mailbox Peport, a Return message type indicates that a return message was automatically placed in the mailbox of the sender of the original message; an Acknowledge message type indicates that the recipient had played the sender's message.