ProFTPD listen only on one specific IP address

To tell ProFTPD only to listen on one specific IP address you need to set the following configuration parameters in your proftpd.conf file.

If the IP address is the first IP address of your system:

SocketBindTight                 on

If the IP address should be explicitly defined:

SocketBindTight                 on
DefaultAddress                  127.0.0.1

The ProFTPD documentation isn't very clear in this question, so I decided to post this article.