Hello ink0gnito,
Has anybody an idea?
First of all, the address shown for your online.net FTP server (123.456.123.23) is not a real IP address; have you “redacted” it before posting here, or was it really that address that was being shown? Probably the former, but if the latter, I would suspect you got a bad address somewhere in your configuration.
If the former, it seems that your online.net FTP server is simply refusing connections from your client; FTP is a really antiquated and messy protocol which (unlike most modern protocols) require new “backchannel” connections for some of the data to flow from the server to the client, for example the “ls” command which would list the remote files. In this vein, the problem would be probably related to the inability of the server to provide “passive mode” FTP, which is what rclone uses (see here for more details). You could debug this by using a conventional FTP client and forcing passive mode on it, then trying to connect to the online.net server.
Either way, my suggestion is to use something else instead of FTP (for example, SFTP) if online.net allows; this would not only be more secure (FTP sends your password in plaintext on the wire) but faster (specially for lots of small files) and possibly more stable.
Cheers,
– Durval.