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SRS?

2019-03-21
2019-03-21
  • Rainer Sokoll

    Rainer Sokoll - 2019-03-21

    Hi,

    this log:

    Mar 20 04:15:09 mx2 postfix/cleanup[10493]: 2E5F7610B4: milter-reject: END-OF-MESSAGE from o1.f.az.sendgrid.net[208.117.55.132]: 5.7.1 rejected by DMARC policy for example.com; from=<bounces+4491766-4033-jdoe=example.com@sendgrid.net> to=<jdoe@example.com> proto=ESMTP helo=<o1.f.az.sendgrid.net>
    

    (original domain replaced with example.com)
    I do not understand much about SRS, but it seems to me sendgrid uses SRS here to rewrite the original sender's address (jdoe@example.com).
    So my question is: Why opendmarc rejects this address?

    Debian stable with opendmarc 1.3.2-2+deb9u1

    Thank you,

    Rainer

     
    • Dominic

      Dominic - 2019-03-21

      On Thu, 21 Mar 2019 at 13:02, Rainer Sokoll rsokoll@users.sourceforge.net
      wrote:

      Hi,

      this log:

      Mar 20 04:15:09 mx2 postfix/cleanup[10493]: 2E5F7610B4: milter-reject: END-OF-MESSAGE from o1.f.az.sendgrid.net[208.117.55.132]: 5.7.1 rejected by DMARC policy for example.com; from=bounces+4491766-4033-jdoe=example.com@sendgrid.net to=jdoe@example.com proto=ESMTP helo=<o1.f.az.sendgrid.net></o1.f.az.sendgrid.net>

      (original domain replaced with example.com)
      I do not understand much about SRS, but it seems to me sendgrid uses SRS
      here to rewrite the original sender's address (jdoe@example.com).
      So my question is: Why opendmarc rejects this address?

      Debian stable with opendmarc 1.3.2-2+deb9u1

      The 'from=<..>' address in that log entry is the envelope sender not the
      address that appears in the 'From' header. DMARC tests against the address
      in the 'From' header. I admit the log entry could be clearer.

       
      • Rainer Sokoll

        Rainer Sokoll - 2019-03-21

        Are you sure that opendmarc tests NOT against the envelope-from?
        Isn't SRS made exactly for rewriting the envelope-from and not the header-from?

        And is there anything I can do here (operator of the rejecting mail server)?

         
        • Dominic

          Dominic - 2019-03-21

          On Thu, 21 Mar 2019 at 13:52, Rainer Sokoll rsokoll@users.sourceforge.net
          wrote:

          Are you sure that opendmarc tests NOT against the envelope-from?
          Isn't SRS made exactly for rewriting the envelope-from and not the
          header-from?

          And is there anything I can do here (operator of the rejecting mail
          server)?

          For an explanation about DMARC see, for example:
          https://www.sparkpost.com/resources/email-explained/dmarc-explained/

          You haven't provided full details and have obfuscated, but it looks like
          the problem is with the originator, so really you shouldn't do anything. Do
          you even know that these are genuine emails? According to the originator's
          DMARC rules, they are not. FYI, changing the envelope sender does not
          break DKIM (and does not therefore necessarily cause DMARC failure). It
          will however break SPF alignment, so that DMARC pass then depends on DKIM
          pass (which is a good thing). Changing or reformatting the body of the
          email, or modifying certain headers, will break DKIM.

          If you are confident the emails are genuine you should contact the
          originator and explain the problem to them. Most recipients of their emails
          will have the same problem (because all the big email providers honour
          DMARC on incoming mails).

           
          • Rainer Sokoll

            Rainer Sokoll - 2019-03-21
            Post awaiting moderation.

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