How to check for unsent email

var
    Outbox: MAPIFolder;
    UnsentMail: integer;
  ...
    Outbox := NmSpace.GetDefaultFolder(olFolderOutbox);
    UnsentMail := Outbox.Items.Count;
    if (UnsentMail > 0) then
      ShowMessage(Format('Unsent items in Outbox: %d', [UnsentMail]));

The constant olFolderOutbox is defined in Outlook_TLB as $00000004