Probably not omv related, but i have issues with changing ftp port.
Port 21 works fine also from the internet with port forwarding.
Changing the portnumber to something like 21000 (and also the portforwarding) gives unreliable or no access.
I also tried the outside port of 21000 and internal port 21 (with the correct portforwarding) but that does not work either.
Do i miss something? I read about ftp port 21 being a control port only?