OK. It is obviously problematic to use the active mode, if your external IP address is changing.
I might implement automatic detection of the external IP address.
But as no one really uses the active mode these days, it does not have a high priority. Sorry.

Sorry! The "Guest" here above is "RobiFlower", who failed to log in.

martin wrote:

So, is it an official policy of the FTP server that is does not support passive mode? As you talk about a mandatory active mode.

Yes, it is the official policy of UNIMI to impose the active mode ("Active mode is the only mode to access our server ...").
The basic information they provide for their server is this:
---------------------------------
Linux version: "Red Hat Enterprise Linux v.5, kernel 2.6.18"
Http server Apache version: 2.2.8
PHP: vers. 5.3.6
MySql: vers. 5.0.22
---------------------------------

So, is it an official policy of the FTP server that is does not support passive mode? As you talk about a mandatory active mode.

I opened my firewall to allow the active mode and I created a rule to have all ports open in Windows dynamic port range 49152 - 65535. No luck!
I’m giving it up because my public address changes every time I reconnect, so even if the procedures you suggest were successful, the thing would be far too laborious.
In the future perhaps you will find an automatic procedure to overcome the obstacles of a mandatory active mode. Possibly by combining the techniques of an online connection (which works for me) with the structure of a good client like WinSCP?
Anyway I’m attaching a log to show that connection fails in passive mode, in the hope that you can help that way. In any case I’m very thankful for what you’ve done fo far.

RobiFlower wrote:

Active mode is mandatory.

So did you open a firewall to allow the active mode?
See https://winscp.net/eng/docs/ftp_modes

And if I try passive mode, the connection fails.

Show us a log for that.

I've told WinSCP my public IP address, but to no avail. I've also tried the connection in active mode from another PC: no luck.

Show us a log for that.

Any reason you use an active mode? Did you try a (default) passive mode?
See https://winscp.net/eng/docs/ui_login_connection
If you need to use the active mode, you have to tell WinSCP your public IP address:
https://winscp.net/eng/docs/ui_pref_network
----------------------------------------------
Active mode is mandatory. And if I try passive mode, the connection fails.
I've told WinSCP my public IP address, but to no avail. I've also tried the connection in active mode from another PC: no luck.

Any reason you use an active mode? Did you try a (default) passive mode?
See https://winscp.net/eng/docs/ui_login_connection

If you need to use the active mode, you have to tell WinSCP your public IP address:
https://winscp.net/eng/docs/ui_pref_network

I use WinSCP 5.7.4 (Build 5553) on Windows 8.1 professional (always updated). Transfer protocol: FTP. GUI: Commander. Error message: Error listing directory '/public_html'. - Could not retrieve directory listing - Illegal PORT command.
I can see the remote directory on the right-hand panel, but the listing does not show. I’ve tried various settings, but the problem persists. I've also disactivated my firewall and antivirus. I'm attaching a *.log.
Thank you for your kind attention!

P.S.: I can see '/public_html' with all its files when I use an online FTP service. Thanks!