<quote who="[EMAIL PROTECTED]">

> One that accepts the incoming tcp port 25, and then does the checks in 
> realtime.

Every modern MTA should do this, indeed, even decidedly unmodern MTAs do. ;)

> ie:
> EHLO; mail
> <check with rbl lists if IP or reverse lookup is an open relay, if so, 
> send a  530 Access Denied and exit>
> 250 myserver
> MAIL FROM: <[EMAIL PROTECTED]>
> <check system wide blacklist, if exists, then send 530 Access Denied and 
> exit>
> 250 Ok
> MAIL TO: <[EMAIL PROTECTED]>
> <check user blacklist, if exists, then send a 550 recipient address 
> rejected>

Lots of fun policy stuff for every step of the SMTP dialogue:

  http://www.postfix.org/uce.html

> 250 Ok
> DATA
> Then compare the data line by line, and if it is considered spam status, 
> stop it at that line with a 530 Access Denied and Exit.

This starts getting dangerous, particularly if you're using another piece of
software to do the checking (highly likely). postfix has a content filtering
system that hands off the email after accepting it, and you can also use the
simpler regexp header_checks and body_checks (and limit the amount of body
data checked, so you're not running regexps over every line of every email).

- Jeff

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