On Wed, Nov 23, 2011 at 03:23:11PM +0100, Mark Martinec wrote:
> Wietse wrote:
> > To make per-recipient end-of-data replies useful with Postfix, PRDR
> > would need to be supported by at least one third-party content
> > inspection mechanism (such as Amavisd-new or Milter), because I see
> > no obvious user interface for PRDR with Postfix header/body_checks.
> >
> > - SMTP-based filters such as Amavisd-new would use the PRDR protocol
> > to send per-recipient end-of-data replies.
>
> If postfix implements PRDR, then I can add it to amavisd too.
>
> Alternatively, if smtpd_proxy_filter would automagically speak
> LMTP to a filter, than I needn't change anything, as amavisd
> already speaks either SMTP or LMTP, both on input and output.
Postfix has no assurance that an "LHLO" sent via the proxy that
receives a 250 reply was actually understood by the proxy and the
proxy is willing to talk LMTP. The proxy I wrote will pass unknown
commands and return unknown responses, under the assumption that
it only cares about "MAIL", "RCPT", "DATA" and "DOT" (yes it peeks
at XFORWARD too) so anything else is just let through.
Provided the protocol is still SMTP, all's well. If the protocol
suddenly becomes LMTP, that would be a problem.
It is not easy to discover what a *transparent* proxy is capable of.
The very transparency can hide this information. So caution is required.
--
Viktor.
