How to limit the ability to connect to the server from the outside?
I have an external IP, port 8080 is redirected to the Qunap file server. How to limit the possibility of connecting to an external server for selected computers? The best way to do it is through MAC. I have read other forums but I can not find the right place to enter these addresses.

Hi

MAC based filtering is only useful for limiting access in same network / subnet.

What I've understood is that the external router is port forwarding connection to an internal ip.
If you use that forward from specific locations, you could update the forward rule to only apply for specific ip's or ranges.

If external connections can come from anywhere, you should look into VPN setup, as it will provide you authenticated access over secured channel.

In addition to @sebastia suggestion of using address list, you can use port knocking to add IPs to your address list.
https://wiki.mikrotik.com/wiki/Port_Knocking

@pawelek5 You posted this on the Wireless Networking forum. Do you mean "from the outside" in a wireless sense? You will probably get more help in the General forum if you have a general networking question not involving radios.