If your server has multiple IP addresses, then you need to way to specify one of those addresses for outgoing connections or use the default one. To address this I had to create a small patch:
Debian GNU/Linux contains a command line based FTP client, which has been enhanced to understand the AUTH SSL command. This is a good thing, but AUTH SSL has been superseded by AUTH TLS. At least one server, pure-ftpd, only understands the latter, because it does not support encrypted data transfers (which is mandatory for AUTH SSL), but only encrypted control connections. This patch adds AUTH TLS to ftp-ssl.