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Re: Backscatter Mail

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  • Viktor Dukhovni
    ... This is not generally possible. POP3 does not record the envelope addresses, and resending mail to the To: and Cc: addresses of already delivered mail
    Message 1 of 3 , Jul 31, 2013
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      On Wed, Jul 31, 2013 at 09:31:20PM -0400, Roman Gelfand wrote:

      > We are running an application which pulls mail from yahoo pop3 server
      > and ultimately resends it, via local postfix server, keeping the same
      > from and to addresses.

      This is not generally possible. POP3 does not record the envelope
      addresses, and resending mail to the "To:" and "Cc:" addresses of
      already delivered mail is a disaster in the making. Duplicate
      deliveries, mail loops, ...

      The only thing that is safe to do is to deliver to a fixed local
      address that is associated with the remote mailbox.

      Can you explain how you determine which addresses to redeliver to?

      > The way I see it, there are rare instances
      > where from domain requires strict dkim enforcement. As a result,
      > yahoo rejects it notifying this postfix server.

      DKIM signs content. If you don't modify the message, its DKIM
      signature remains valid.

      It sure sounds like you're doing something unusual or even unwise.
      What real problem are you solving?

      --
      Viktor.
    • Roman Gelfand
      Actually, the program a) grabs pop3 object b) parses it c) modifies subject slightly with certain keywords based on email contents d) based on it builds smtp
      Message 2 of 3 , Jul 31, 2013
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        Actually, the program a) grabs pop3 object b) parses it c) modifies
        subject slightly with certain keywords based on email contents d)
        based on it builds smtp object. Hence, the from and to of the smtp
        object is being assigned by from and to of the parsed pop object. So,
        it is not a resend. The to address is always email from our domain
        which is hosted by yahoo.

        The reason why we need to send to the same from and to addresses is
        for agents to process email based on an outlook folder determined by
        subject rule. Also, these agents need the ability to respond to these
        emails.

        As I am writing to you, I am thinking a) I should create mail store
        locally for the same domain. b) create mx record for the domain only
        on the local(ie no outside box is using this dns server) postfix
        server c) point deliveries via lmtp to mail store.

        Please, let me know if this sounds right.

        I didn't plan it. I inherited it. Though there are very few of these
        occurrences, I am concerned now that we may get blacklisted for
        something like this.



        On Wed, Jul 31, 2013 at 9:38 PM, Viktor Dukhovni
        <postfix-users@...> wrote:
        > On Wed, Jul 31, 2013 at 09:31:20PM -0400, Roman Gelfand wrote:
        >
        >> We are running an application which pulls mail from yahoo pop3 server
        >> and ultimately resends it, via local postfix server, keeping the same
        >> from and to addresses.
        >
        > This is not generally possible. POP3 does not record the envelope
        > addresses, and resending mail to the "To:" and "Cc:" addresses of
        > already delivered mail is a disaster in the making. Duplicate
        > deliveries, mail loops, ...
        >
        > The only thing that is safe to do is to deliver to a fixed local
        > address that is associated with the remote mailbox.
        >
        > Can you explain how you determine which addresses to redeliver to?
        >
        >> The way I see it, there are rare instances
        >> where from domain requires strict dkim enforcement. As a result,
        >> yahoo rejects it notifying this postfix server.
        >
        > DKIM signs content. If you don't modify the message, its DKIM
        > signature remains valid.
        >
        > It sure sounds like you're doing something unusual or even unwise.
        > What real problem are you solving?
        >
        > --
        > Viktor.
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