docs: @Nonnull
    public static EChange setMailQueueSize (@Nonnegative final int nMaxMailQueueLen,
                                            @Nonnegative final int nMaxMailSendCount)
    {
      ValueEnforcer.isGT0 (nMaxMailQueueLen, "MaxMailQueueLen");
      ValueEnforcer.isGT0 (nMaxMailSendCount, "MaxMailSendCount");
      ValueEnforcer.isTrue (nMaxMailQueueLen >= nMaxMailSendCount,
                            () -> "MaxMailQueueLen (" +
                                  nMaxMailQueueLen +
                                  ") must be >= than MaxMailSendCount (" +
                                  nMaxMailSendCount +
                                  ")");
  
      return s_aRWLock.writeLocked ( () -> {
        if (nMaxMailQueueLen == s_nMaxMailQueueLen && nMaxMailSendCount == s_nMaxMailSendCount)
          return EChange.UNCHANGED;
        s_nMaxMailQueueLen = nMaxMailQueueLen;
        s_nMaxMailSendCount = nMaxMailSendCount;
        return EChange.CHANGED;
      });
    }