[vox-tech] Anyone running a mail server on a dynamic IP?

[Rick Moen]

Quoting Rod Roark (rod at sunsetsystems.com):

> Postfix's built-in spam controls (such as RBL checks)
> operate like this.  In the past, for 3rd party filters like
> SpamAssassin you had to accept the mail first; but if you
> use the above-mentioned "before queue" interface, you can
> presumably invoke stuff like SpamAssassin and ClamAV while
> the SMTP connection is still active.
 
Postfix's policy-daemon interface is quite useful, which is how one is
able to do SPF checks at SMTP time, for example.

What one misses is Exim4's advanced callout functions, which one can use
to conduct automated test checks during the SMTP session, e.g., to
ensure that claimed sender's domain accepts mail to the required
postmaster@ and abuse@ addresses, that it accepts mail as required from
sender "<>", and that the alleged sender's e-mail address is deliverable
-- all prior to (programmatically) deciding whether to accept the mail
under delivery or not.

Thus, your system can conduct those (in my experience _highly_ useful) 
checks and issue a meaningful Delivery Status Notification (SMTP error
code and text message), accordingly.  Something like:

550  Delivery refused, because the alleged sender domain lacks a postmaster 
550  address as required by RFC2821.

-- 
Cheers,           find / -user your -name base -print | xargs chown us:us
Rick Moen
rick at linuxmafia.com