[Cooker] ADSL + postfix default config = open relay?

[Bruno Prior]

My ISP has just pointed out to me that I was running an open relay, 
which is highly embarrassing. I have been running postfix without 
causing a problem until I switched to an ADSL connection. The notes in 
postfix/main.cf seem to make it pretty clear what the problem is: my 
ISP's subnet had been added as a trusted subnet, as ADSL counts as a 
dialup connection, which meant that anyone on their network could relay 
through my mail server.

Obviously, the fault is principally mine, for not being more careful 
when I set ADSL up - the information is all there if you look for it. 
But I was wondering how many people would look for it. Because, if you 
setup ADSL using drakconnect, you wouldn't have a clue you needed to 
edit main.cf to prevent this. Would it be a good idea to either enhance 
drakconnect to make this change automatically (if you could figure out a 
sensible way to deduce the appropriate list of trusted clients), or at 
least flag up a warning, to stop other people making this mistake?

Cheers,

Bruno Prior