If incoming, the author that sent the message, if the message was sent in a channel. If outgoing, undefined.
The contact that sent or received the message. If this is a channel message, the contact will be the channel.
Whether the message was received or sent.
The text body of the message.
The timestamp of the message.
A Zello alert message. Alert messages contain text and are typically used for important messages. They will play a recurring sound until the user acknowledges them by bringing the app to the foreground.