IP bans although immune set

[Yil]

ioFTPD doesn't support the CCSN command and it isn't advertised as supported by FEAT. In fact, I had not even heard of that command prior to you mentioning it. It appears to be identical to the SSCN command which is popular, supported, and listed in the default FEAT response. Can you double check you didn't misread the FEAT response?

I think most FTP clients know about SSCN, but if you have one that only wants to use CCSN it would be trivial to add since the functionality is the same.