The value of the Sender header field of the Message.
property Sender: TsbxMailAddress read get_Sender;
This field specifies the mailbox of the agent responsible for the actual transmission of this message.
If the originator of the message can be indicated by a single mailbox and both the author and the transmitter are the same entity, the "Sender:" field is not used ("From:" used instead).
This property is read-only.