OK, let’s fire up the truck and cycle through the whole stuff step by step 
Prior to the following, you have to enable the port forwarding inside your router. The example below is bound to port 21 only for Passive Mode FTP.
Entry point is the web interface of the My Cloud at Settings → Network
FTP Access ON, then “Configure>>”
First page of the FTP settings with limitation of the amount of concurrent connections, Idle time of open conenctions and standard port (don’t change this):
Next screen, Passive Mode; best experience if you don’t change anything:
next screen, fine tuning:
Client language deafult is UTF-8 support, best experience to keep this “as is” as almost all characters are supported. Personal tipp: Switch ON the FXP, File Exchange Protocol for the best performance, otherwise the FTP daemon will not use the full bandwidth (important for internal network FTPing)
Add-on to the client laguages, there are much more supported than UTF-8 only:
Last page of the settings, blacklisted IP addresses an exclusion period:
blocking period can be adjusted:
So far, so good, but we shall open the Port Forward rules too. Therefore scroll down to the end of the Settings → Network page and open the Port Forwarding:
Click Add to open and stay on “Select the default service scan”:
Select the FTP service for port 21 only - this is the FTP server in passive mode. If you want to enable Active Mode FTP server, you have to enable port 20 here too. Not recommended unless you know why Active Mode FTP shall be used. Active Mode FTP does not mean that the FTP will work faster than passive.
Click Finish and wait until the rule is applied:
If your port forwarding rule in your router was configured correct prior to the steps described here, then you will see the Status message “Success” if you click on “Details”. This will check if your FTP server can be reached from outside your network:
