[ILUG] Postfix, relayhost & pop-before-smtp

[Stephen Flinter]

Calling all postfix gurus out there.

Due to more and more mail servers refusing mail originating from a 
dynamic IP address, I am forced to rethink the configuration on my home 
mail setup (RedHat running postfix, with pop-before-smtp, on NTL cable 
broadband).

The general wisdom appears to be that you should relay through your 
ISP's SMTP server - in my case smtp.ntlworld.ie.  When I make that 
change to the postfix config it is clear from the logs that the mail is 
being relayed as I want.  However, it appears that ALL inbound mail is 
being relayed, not just mail that has already been authenticated with 
pop-before-smtp.

What I'm trying to do is to ensure that ONLY that mail that has already 
been authenticated via pop-before-smtp will be relayed to 
smtp.ntlworld.ie, and that all other (spam) mail will be rejected at my 
own SMTP server, and not get relayed at all (lest NTL think that I'm the 
ultimate source of the spam).

Does anybody have the appropriate postfix incantation to achieve that?

Thanks,

Steve