Postfix not relaying mail from computers in my network

[xlargebear at bellsouth.net]

Hi
I've previously set up postfix in my mac running MacOS 10.3 to relay 
mail from all computers in my network. It used to work. Now I have 
another mac running YDL4 and I am trying to configure Postfix to do the 
same. As long as I send the emails from the host running Postfix I have 
no problem. However, when I configure the other computers to relay 
through the mail server, I get an error saying "The attempt to read 
data from the server '192.168.1.20' failed". In the logs for Postfix 
nothing shows. I turned off all firewalls and still nothing happens.

myhostname is set my FQDN
mydomain is set to FQDM minus the first part.
myorigin = $mydomain
mydestination = $myhostname, localhost.$mydomain
mynetworks = 192.168.1.0/255, 127.0.0.0/8 ( I also tried 
mynetworks_style = subnet )

If I open a tunnel from any computer to the mail host using ssh -L 
25:127.0.0.1:25 root at mailhost_IP and I set the client to relay through 
127.0.0.1 it works. Why doesn't it work when I enter the actual IP of 
the mail server in the client configuration as the smtp relay host?
Help
Thanks
F