the Sent property sets filtering on whether or not a message was sent through the MAPI system. Read/write.
objMessageFilter.Sent
Boolean
a message's Sent property is True if it was sent through the MAPI system and False if it was posted or saved.
In general, there are three different kinds of messages: sent, posted, and saved. Sent messages are traditional e-mail messages sent to a recipient or public folder. Posted messages are created in a public folder. Saved messages are created and saved without either sending or posting. For more information, see the Message object's Sent property.