If you run a firewall on your Debian  server and want to use passive FTP connections, you have to define the passive port range in pure-ftpd and your firewall to ensure that the connections dont get blocked.

The following example is for pure-ftpd on Debian Squeeze:

Configure pure-ftpd:

echo "50000 50120" > /etc/pure-ftpd/conf/PassivePortRange

/etc/init.d/pure-ftpd restart
Restarting ftp server: Running: /usr/sbin/pure-ftpd -l pam -l 
puredb:/etc/pure-ftpd/pureftpd.pdb -p 50000:50120 -O
clf:/var/log/pure-ftpd/transfer.log -S,2121 -8 UTF-8 -H -u 1000 -E -B