I'm trying to use the Message ID property on a mailbox item to determine whether it's a journaled or non-journaled item.
When I say non-journaled I mean, calendar events, contacts, drafts.
Is this the right thing to do? Is the Message ID assigned when the item is sent?
The Messsage ID is assigned to the $MessageID item by the router when the message is submitted to be sent. A calendar event will not contain a $MessageId, but a calendar invitation or calendar notice will, because they are processed by the mail system.
However, the presence of a $MessageId item does not necessarily mean the message was mailed to or by the specific mailbox that you are looking at, because a message can easily be copied and pasted between mailboxes.
And it's also true that the absence of a $MessageID does not necessarily mean it wasn't mailed, either. I am almost certain that I've seen cases where messages in a user's Sent folder, and which were actually sent, didn't have the $MessageID. I can't recall the circumstances for that, though. (It's pretty easy for a knowledgeable user to remove the $MessageID item from a message by running a simple agent, so that's an obvious reason why you can't count on the $MessageId being there, but that's not the case I'm thinking of.)(