FTP/SSL through a NAT firewall

This was a helpful article in understanding connectivity issues when attempting to use FTPS through a NATed firewall:

http://geekswithblogs.net/Lance/archive/2005/08/23/50912.aspx

I'm using FileZilla Server to receive files from someone else and needed to set up FTPS. Specifying a particular port, and then opening that port, solved the problems I was having (i.e. 425 errors).