If you are you referring to the Message.Sender then you can find more information of the object in Object API documentation.
Message.Sender is an Address type object. See the Address object for more information. The available properties are: DisplayName, EmailAddress, ObjType, etc.
The parameter “Sender” is Delphi object which references the control that was used to call the method. For example, if you click on the Button1 control, causing the Button1Click method to be called, a reference or pointer to the Button1 object is passed to Button1Click in the parameter called Sender.
