Given a mailItem which has .Sent = True, I want to determine whether it
was outbound (ie sent from this mailbox), or inbound (ie sent to this
mailbox).

I can't rely on the location of the message, because it may have been
moved from the Inbox or from Sent Items. I'm also not keen on using
the sender/recipient addresses, because of the possibility of someone
changing their sender address, or sending an email to themselves.

Testing for the presence of PR_RECEIVED_BY_ADDRTYPE seems to work:

Public Function IsInboundMessage(itm As Outlook.MailItem) As Boolean
Dim ssn As New MAPI.Session
Dim msg As MAPI.Message
Dim typ As String

ssn.Logon , , False, False, 0 ' Use the existing Outlook session
Set msg = ssn.GetMessage(itm.EntryID, itm.Parent.StoreID)

On Error Resume Next
typ = msg.Fields(CdoPR_RECEIVED_BY_ADDRTYPE).Value

If Err.Number 0 Then
Err.Clear
IsInboundMessage = False
Else
IsInboundMessage = True
End If

On Error GoTo 0

ssn.Logoff
Set ssn = Nothing
Set msg = Nothing
End Function

Is this the right way to do this? And is it reliable?

Thanks.

Andy Bowles