When I say NAT, I mean NAT as in when data is coming out the egress point of a router and it gets translated to a different address. Anything to do with inbound/outbound rules typically relate to firewalls. As I don't really know what your network layout is like, it does make it pretty difficult to troubleshoot. Typically in non-home networks there will not be any NAT accept at the border gateway/firewall. If any clients are connecting to the FTP server from outside your network then you will need both inbound firewall rules to permit the traffic into your network and forwarding rules so the traffic can get to the server. If the clients are on the same LAN as the server they will need inbound rules for 21 and the data ports on the server provided it has a firewall. If the the clients are on a different LANs then you will need that traffic to be routable to the server's LAN, and the firewall rules on the server (inbound)