public ImapSequenceSet GetSequenceOrUidSet(ImapOpenedMailboxInfo mailbox)
            {
                mailbox.Refresh();

                if (mailbox.ExistMessageCount <= 0L)
                  return ImapSequenceSet.CreateSet(new long[0]);
                else
                  return ImapSequenceSet.CreateRangeSet(1L, mailbox.ExistMessageCount);
            }