1. A method for dynamic modification of allowable electronic message properties, comprising: composing an electronic message by entering data in various fields of the message and selecting messaging properties from a list of available property options to apply to said message; automatically updating said list of property options available to be applied to said message based on contents of the message entries made by a user and system policies applicable to said contents; displaying an updated list of property options available to be applied to the message to the user based on the results of the automatic updating step; selecting a property to apply to the message from the updated list of property options; and sending the message having the selected property options applied thereto.