Yes there is. I firstly planned place sub server (other user's severs) mechanism which receives messages as same as main server and these can pass data to main

Yes there is. I firstly planned place sub server (other user's severs) mechanism which receives messages as same as main server and these can pass data to main server when it become online. But it is complicated to implement. So, it is not implemented now. Additionaly, accumulating messages from following users servers when become online can be implemented. But, this feature leads non ignoreable increase of machine/network resource consumption. So this is not implemented too.