SharingItem.Sent Property (Outlook)
Returns a Boolean value that indicates if the SharingItem has been sent. Read-only.
In general, there are three different kinds of messages: sent, posted, and saved. Sent messages are items 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.
If this property is set to True, attempting to set the SendUsingAccount property raises an error.