# File lib/rfilter/deliver.rb, line 42
    def deliver_mbox(filename, message)
      return filename if filename == '/dev/null'
      File.open(filename,
                File::RDWR|File::CREAT|SYNC_IF_NO_FSYNC,
                0600) { |f|
        max = 5
        max.times { |i|
          break if f.flock(File::LOCK_EX | File::LOCK_NB)
          raise LockingError, "Timeout locking mailbox." if i == max - 1
          sleep(1)
        }
        st = f.lstat
        unless st.file?
          raise NotAFile,
            "Can not deliver to #{filename}, not a regular file."
        end
        unless is_an_mbox(f, st)
          raise NotAMailbox,
            "Can not deliver to #{filename}, file is not in mbox format."
        end
        begin
          # Ignore SIGXFSZ, since we want to get the Errno::EFBIG
          # exception when the file is too big.
          old_handler = trap('XFSZ', 'IGNORE') || 'DEFAULT'
          write_to_mbox(f, message)
          begin
            f.fsync
          rescue NameError
            # NameError happens with older versions of Ruby that have
            # no File#fsync
            f.flush
          end
        rescue Exception => e
          begin
            begin
              f.flush
            rescue Exception
            end
            f.truncate(st.size)
          ensure
            raise e
          end
        ensure
          if old_handler
            trap('XFSZ', old_handler)
          end
        end
        f.flock(File::LOCK_UN)
      }
      filename
    end