1.2.10rc1 and later
When configuring proftpd, it is sometimes nice, or even necessary, to tag or label a client as belonging to some group, based on that client's IP address or DNS hostname. A "class" is the name for such connection-based groupings in ProFTPD terms. A class is defined to have a name, and as having certain criteria such as IP addresses, IP subnets/masks, and DNS hostnames. A client that connects to the daemon that has matching characteristics is then labeled as belonging to that class.
Within a <Class> section, the From directive is used to list the IP addresses, IP subnet/masks, and DNS names that make up the class.
This defines a class named "internal"; any client connecting from 192.168.0.0/16 will belong to this class. And if you wanted to define a class for all clients not connecting from 192.168.0.0/16 address space:
A more complicated class might include matching DNS names as well:
From 220.127.116.11 From proxy.*.com From my.example.com From 18.104.22.168