291358Re: Null sender address in NDR's
- Feb 14, 2013On Thu, Feb 14, 2013 at 03:36:11PM +0000, James Day wrote:
> > > Is there a sensible way to configure postfix to allow these messagesThis has nothing to do with spam. One can just as easily send spam
> > > with null sender addresses to be relayed without opening the smart
> > > host up to exploitation?
> > Sending bounces is not "exploitation", but the "smart host" (really
> > submission service) policy is up to the ISP. Ask them.
> I wasn't trying to suggest that sending bounces would be
> exploitation, rather that allowing *all* messages with a NULL sender
> to relayed through could potentially be exploited to send spam as <>
as <malory@...> as one can as <>. The ISP can equally easily
track it down, since the Received: headers will contain the offending
The real issue is that the ISP offering a consumer-grade submission
service for MUAs, not a relay service for MTAs. Their rate limit
policies may be based on sender domains, rather than client IP
addresses (ideally they should really use the SASL login name).
Perhaps a business-grade service offering from the same ISP
(typically at a higher price-point) offers ISP support, or a
static sending IP not listed in the PBL (in which case simply
send direct and don't use the ISP relay).
> > > And before anyone comments, yes I know this isn't best practice asNot in this case, sending NDRs with a non-null envelope sender
> > > NDR's should have null sender addresses to stop loops (bouncing
> > > bounce-backs!).
> > Not "should", MUST. Not "isn't best practice", rather prohibited.
> I understand and agree however in my experience you sometimes
> have to fudge things so they operate with incorrectly configured
> systems (against my own wishes!)
address is a fundamental violation of the robustness requirements
of SMTP. This goes beyond working-around misconfiguration to flagrant
violation of a basic design requirement that prevents congestive
collapse of the mail system.
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