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291357Re: Null sender address in NDR's

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  • Robert Schetterer
    Feb 14, 2013
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      Am 14.02.2013 16:36, schrieb James Day:
      > .
      >>> 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.
      > 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 <>
      >> 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.
      > Yes I know that and have referred to that point below.
      >> The solution is to use a relay that permits bounces. Either the ISP relaxes
      >> their policies, or a different relay must be found.
      > As I feared, thank you for confirming.
      >>> 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.
      > 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!)
      > James

      looking in my relayhosts for exchange, i see <> is accepted via
      submission tls if sasl auth is done before
      from exchange with reject_sender_login_mismatch ,
      smtpd_sender_login_maps exists, this should be enough for the smarthost
      isp , i only know the problem apearing with i.e static restrict tables

      Best Regards
      MfG Robert Schetterer

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