On Thu, Feb 14, 2013 at 03:03:23PM +0000, James Day wrote:
> A customer of mine is using a smart host provided by their ISP
> through which all outbound mail is delivered smtp.enta.net (which
> is running postfix).
This ISP's outbound relay is a submission service that is *only* suitable
for relaying email from MUAs.
> The problem is that when clients mail server sends a NDR the
> sender address is <> (ie NULL). The null sender address causes the
> message to be rejected with:
The relay does not support MTAs.
> Is there a sensible way to configure postfix to allow these
> messages 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.
> Or alternatively - and this is off topic for this list - is there
> a way to configure Microsoft exchange 2003 to send NDR's with a
> different sender address.
NO. Bounces MUST be sent with a null sender address. Otherwise,
bounces would elicit bounces in return creating mail loops, sometimes
exponentially growing, if a message elicits multiple non-delivery
reports.
The solution is to use a relay that permits bounces. Either the ISP
relaxes their policies, or a different relay must be found.
> And before anyone comments, yes I know this isn't best practice
> as NDR's should have null sender addresses to stop loops (bouncing
> bounce-backs!).
Not "should", MUST. Not "isn't best practice", rather prohibited.
--
Viktor.
