Specifies message signature type.
Use this property to specify the signature type of the message.
If the property value is
True than any user will be able to read the message.
If the program that can't process signatures is used there is no way to check the signature but it is still possible to read the message.
When this signature type is used the content-type of the message is
If the second signature type is used (the property value is False), the program will be able only to show an attachment. This signature type makes the message better protected against damages during passing the mail servers than the first one. When this signature type is used the content-type of the message is 'application/pksc7-mime; smime-type=signed-data'.
Default value is True.