Thanks a lot for your kind replay.
So I have deleted the proxy ftp service on Wingate (as a first step) hoping it would be possible to connect directly to my ftp server (GuildFTP) running on my pc...
but no luck, I can see the user attempting to connect in GuildFTP program, but he gets no listing of the directory.
When I do this locally in my little network from another pc I succeed in typing:
ftp://user:password@172.16.1.1. ...everything is ok
I have forwarded port 21 (is it enough ?) to the ftp server, but I have no idea what to do else...there is no extra firewall between me and my "guest".
Will keep on trying....next time I will take a look at the firewall report to see if there is any hit.
Greetings
Christian