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Re: backupmx with Postfix

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  • Nicolas Letellier
    On Tue, 01 Jul 2008 11:04:53 +0200 ... But, if Postfix rejects a mail, it sends a mail to inform that the mail has been rejected or not? If rejecting a mail,
    Message 1 of 19 , Jul 1, 2008
      On Tue, 01 Jul 2008 11:04:53 +0200
      mouss <mouss@...> wrote:
      > If you have relay_recipient_maps set, then postfix will _reject_, not
      > bounce. it is the "previous" MTA that generates the bounce. This is why
      > you should reject on the first server that you manage and let others
      > bounce or do whatever they want.
      But, if Postfix rejects a mail, it sends a mail to inform that the mail has been rejected or not?
      If rejecting a mail, Postfix send it to /dev/null and do not send any mails to sender, it's a good news!


      --
      -Nicolas.
    • Mark Goodge
      ... No. The server that has the mail rejected sends the mail. Consider this sequence of events: 1. User sends mail out via server A. 2. Server A contacts
      Message 2 of 19 , Jul 1, 2008
        Nicolas Letellier wrote:
        > On Tue, 01 Jul 2008 11:04:53 +0200
        > mouss <mouss@...> wrote:
        >> If you have relay_recipient_maps set, then postfix will _reject_, not
        >> bounce. it is the "previous" MTA that generates the bounce. This is why
        >> you should reject on the first server that you manage and let others
        >> bounce or do whatever they want.
        >
        > But, if Postfix rejects a mail, it sends a mail to inform that the mail has been rejected or not?

        No. The server that has the mail rejected sends the mail. Consider this
        sequence of events:

        1. User sends mail out via server A.

        2. Server A contacts server B to pass the message on.

        3. Server B accepts the mail.

        4. Server B contacts server C to pass the message on.

        5. Server C rejects the mail.

        6. Server B emails the sender to say that the mail was rejected by C.

        You only need to worry about this if you manage server B (as it makes
        you a potential source of backscatter). If you manage server C, then all
        you need to do is reject mail you don't want.

        Mark
        --
        http://mark.goodge.co.uk - my pointless blog
        http://www.good-stuff.co.uk - my less pointless stuff
      • Nicolas Letellier
        On Tue, 01 Jul 2008 10:42:02 +0100 ... I manage server B (backupmx). Server C is not mine. The problem is: 1. User sends mail out via server A to an non
        Message 3 of 19 , Jul 1, 2008
          On Tue, 01 Jul 2008 10:42:02 +0100
          Mark Goodge <mark@...> wrote:

          >
          >
          > Nicolas Letellier wrote:
          > > On Tue, 01 Jul 2008 11:04:53 +0200
          > > mouss <mouss@...> wrote:
          > >> If you have relay_recipient_maps set, then postfix will _reject_, not
          > >> bounce. it is the "previous" MTA that generates the bounce. This is why
          > >> you should reject on the first server that you manage and let others
          > >> bounce or do whatever they want.
          > >
          > > But, if Postfix rejects a mail, it sends a mail to inform that the mail has been rejected or not?
          >
          > No. The server that has the mail rejected sends the mail. Consider this
          > sequence of events:
          >
          > 1. User sends mail out via server A.
          >
          > 2. Server A contacts server B to pass the message on.
          >
          > 3. Server B accepts the mail.
          >
          > 4. Server B contacts server C to pass the message on.
          >
          > 5. Server C rejects the mail.
          >
          > 6. Server B emails the sender to say that the mail was rejected by C.
          >
          > You only need to worry about this if you manage server B (as it makes
          > you a potential source of backscatter). If you manage server C, then all
          > you need to do is reject mail you don't want.
          I manage server B (backupmx). Server C is not mine.
          The problem is:

          1. User sends mail out via server A to an non existent recipient like 4-ygbG5_ygà@...
          2. Server B checks the recipient and see it does not exists in recipient_maps (so it does not relay it to server C). The mail is rejected.
          3. Is server B send an email to User to inform him that his email has not been received (because of a bad recipient) ?


          --
          -Nicolas.
        • Scott Kitterman
          ... No. That s server A s job. Server B rejects the message and never takes responsibility for it. Server A is still responsible for the message and
          Message 4 of 19 , Jul 1, 2008
            On Tue, 1 Jul 2008 11:53:52 +0200 Nicolas Letellier <nicolas@...> wrote:
            >On Tue, 01 Jul 2008 10:42:02 +0100
            >Mark Goodge <mark@...> wrote:
            >
            >>
            >>
            >> Nicolas Letellier wrote:
            >> > On Tue, 01 Jul 2008 11:04:53 +0200
            >> > mouss <mouss@...> wrote:
            >> >> If you have relay_recipient_maps set, then postfix will _reject_, not
            >> >> bounce. it is the "previous" MTA that generates the bounce. This is why
            >> >> you should reject on the first server that you manage and let others
            >> >> bounce or do whatever they want.
            >> >
            >> > But, if Postfix rejects a mail, it sends a mail to inform that the mail has been rejected or not?
            >>
            >> No. The server that has the mail rejected sends the mail. Consider this
            >> sequence of events:
            >>
            >> 1. User sends mail out via server A.
            >>
            >> 2. Server A contacts server B to pass the message on.
            >>
            >> 3. Server B accepts the mail.
            >>
            >> 4. Server B contacts server C to pass the message on.
            >>
            >> 5. Server C rejects the mail.
            >>
            >> 6. Server B emails the sender to say that the mail was rejected by C.
            >>
            >> You only need to worry about this if you manage server B (as it makes
            >> you a potential source of backscatter). If you manage server C, then all
            >> you need to do is reject mail you don't want.
            >I manage server B (backupmx). Server C is not mine.
            >The problem is:
            >
            >1. User sends mail out via server A to an non existent recipient like 4-ygbG5_ygà@...
            >2. Server B checks the recipient and see it does not exists in recipient_maps (so it does not relay it to server C). The mail is rejected.
            >3. Is server B send an email to User to inform him that his email has not been received (because of a bad recipient) ?

            No. That's server A's job.

            Server B rejects the message and never takes responsibility for it. Server A is still responsible for the message and generating the bounce message.

            Scott K
          • Mark Goodge
            ... No. In this case, server A will send the email, because it will not get to step 3 in my sequence above. Instead, you have this: 1. User sends mail out via
            Message 5 of 19 , Jul 1, 2008
              Nicolas Letellier wrote:
              > On Tue, 01 Jul 2008 10:42:02 +0100
              > Mark Goodge <mark@...> wrote:
              >
              >> No. The server that has the mail rejected sends the mail. Consider this
              >> sequence of events:
              >>
              >> 1. User sends mail out via server A.
              >>
              >> 2. Server A contacts server B to pass the message on.
              >>
              >> 3. Server B accepts the mail.
              >>
              >> 4. Server B contacts server C to pass the message on.
              >>
              >> 5. Server C rejects the mail.
              >>
              >> 6. Server B emails the sender to say that the mail was rejected by C.
              >>
              >> You only need to worry about this if you manage server B (as it makes
              >> you a potential source of backscatter). If you manage server C, then all
              >> you need to do is reject mail you don't want.
              >
              > I manage server B (backupmx). Server C is not mine.
              > The problem is:
              >
              > 1. User sends mail out via server A to an non existent recipient like 4-ygbG5_ygà@...
              > 2. Server B checks the recipient and see it does not exists in recipient_maps (so it does not relay it to server C). The mail is rejected.
              > 3. Is server B send an email to User to inform him that his email has not been received (because of a bad recipient) ?

              No. In this case, server A will send the email, because it will not get
              to step 3 in my sequence above. Instead, you have this:

              1. User sends mail out via server A.

              2. Server A contacts server B to pass the message on.

              3. Server B rejects the mail.

              4. Server A emails the sender to say that the mail was rejected by C.

              Mark
              --
              http://mark.goodge.co.uk - my pointless blog
              http://www.good-stuff.co.uk - my less pointless stuff
            • Nicolas Letellier
              On Tue, 01 Jul 2008 6:04:41 -0400 ... Oops.... I made an error in this message... I retry... Server A: backup MX (me) Server B: smtp.domain.com (true smtp
              Message 6 of 19 , Jul 1, 2008
                On Tue, 01 Jul 2008 6:04:41 -0400
                Scott Kitterman <postfix@...> wrote:

                > On Tue, 1 Jul 2008 11:53:52 +0200 Nicolas Letellier <nicolas@...> wrote:
                > >On Tue, 01 Jul 2008 10:42:02 +0100
                > >Mark Goodge <mark@...> wrote:
                > >
                > >>
                > >>
                > >> Nicolas Letellier wrote:
                > >> > On Tue, 01 Jul 2008 11:04:53 +0200
                > >> > mouss <mouss@...> wrote:
                > >> >> If you have relay_recipient_maps set, then postfix will _reject_, not
                > >> >> bounce. it is the "previous" MTA that generates the bounce. This is why
                > >> >> you should reject on the first server that you manage and let others
                > >> >> bounce or do whatever they want.
                > >> >
                > >> > But, if Postfix rejects a mail, it sends a mail to inform that the mail has been rejected or not?
                > >>
                > >> No. The server that has the mail rejected sends the mail. Consider this
                > >> sequence of events:
                > >>
                > >> 1. User sends mail out via server A.
                > >>
                > >> 2. Server A contacts server B to pass the message on.
                > >>
                > >> 3. Server B accepts the mail.
                > >>
                > >> 4. Server B contacts server C to pass the message on.
                > >>
                > >> 5. Server C rejects the mail.
                > >>
                > >> 6. Server B emails the sender to say that the mail was rejected by C.
                > >>
                > >> You only need to worry about this if you manage server B (as it makes
                > >> you a potential source of backscatter). If you manage server C, then all
                > >> you need to do is reject mail you don't want.
                > >I manage server B (backupmx). Server C is not mine.
                > >The problem is:
                > >
                > >1. User sends mail out via server A to an non existent recipient like 4-ygbG5_ygà@...
                > >2. Server B checks the recipient and see it does not exists in recipient_maps (so it does not relay it to server C). The mail is rejected.
                > >3. Is server B send an email to User to inform him that his email has not been received (because of a bad recipient) ?
                >
                > No. That's server A's job.
                >
                > Server B rejects the message and never takes responsibility for it. Server A is still responsible for the message and generating the bounce message.
                >
                > Scott K
                Oops.... I made an error in this message... I retry...

                Server A: backup MX (me)
                Server B: smtp.domain.com (true smtp server, managed by another persons who want a backupmx)

                1. User sends mail out via server A to an non existent recipient like 4-ygbG5_ygà@...
                2. Server A checks the recipient and see it does not exists in recipient_maps (so it does not relay it to server B). The mail is rejected.
                3. Is server A send an email to User to inform him that his email has not been received (because of a bad recipient) ?

                So, Server A (me) will reject the mail and send a bounce... I don't want to bounce mails for it.


                --
                -Nicolas.
              • mouss
                ... do not confuse reject and bounce . here is a reject example: C is a remote client (MTA or other). S is your server. C- S: connect S- C: show greeting
                Message 7 of 19 , Jul 1, 2008
                  Nicolas Letellier wrote:
                  > On Tue, 01 Jul 2008 11:04:53 +0200
                  > mouss <mouss@...> wrote:
                  >
                  >> If you have relay_recipient_maps set, then postfix will _reject_, not
                  >> bounce. it is the "previous" MTA that generates the bounce. This is why
                  >> you should reject on the first server that you manage and let others
                  >> bounce or do whatever they want.
                  >>
                  > But, if Postfix rejects a mail, it sends a mail to inform that the mail has been rejected or not?
                  > If rejecting a mail, Postfix send it to /dev/null and do not send any mails to sender, it's a good news!
                  >
                  >
                  >

                  do not confuse "reject" and "bounce".

                  here is a reject example: C is a remote client (MTA or other). S is your
                  server.

                  C->S: connect
                  S->C: show greeting banner
                  C->S: says helo
                  S->C: show supported extensions (auth, tls, ... etc)
                  C->S: MAIL FROM: <sender@...>
                  S->C: OK
                  C->S: RCPT TO: <invalid@...>
                  S->C: rejected. recipient does not exist
                  C->S: QUIT

                  no message is exchanged here. your server does nothing after this. it
                  does not send a bounce. If C is a normal MTA, it is its responsibility
                  to generate a bounce, but this none of our business: we don't care.

                  If on the other hand your server is misconfigured, it will accept the
                  mail during the smtp transaction. then later it will find out that it
                  cannot deliver the message. it will then generate a bounce and send it
                  to the original sender. sometime ago, this was ok, but since a lot of
                  spam uses forged addresses, such bounces go to innocent people who did
                  not send anything. This is backscatter.
                • Nicolas Letellier
                  On Tue, 01 Jul 2008 17:33:09 +0200 ... Ok, thanks for the explication! This will help me. -- -Nicolas.
                  Message 8 of 19 , Jul 1, 2008
                    On Tue, 01 Jul 2008 17:33:09 +0200
                    mouss <mouss@...> wrote:

                    > Nicolas Letellier wrote:
                    > > On Tue, 01 Jul 2008 11:04:53 +0200
                    > > mouss <mouss@...> wrote:
                    > >
                    > >> If you have relay_recipient_maps set, then postfix will _reject_, not
                    > >> bounce. it is the "previous" MTA that generates the bounce. This is why
                    > >> you should reject on the first server that you manage and let others
                    > >> bounce or do whatever they want.
                    > >>
                    > > But, if Postfix rejects a mail, it sends a mail to inform that the mail has been rejected or not?
                    > > If rejecting a mail, Postfix send it to /dev/null and do not send any mails to sender, it's a good news!
                    > >
                    > >
                    > >
                    >
                    > do not confuse "reject" and "bounce".
                    >
                    > here is a reject example: C is a remote client (MTA or other). S is your
                    > server.
                    >
                    > C->S: connect
                    > S->C: show greeting banner
                    > C->S: says helo
                    > S->C: show supported extensions (auth, tls, ... etc)
                    > C->S: MAIL FROM: <sender@...>
                    > S->C: OK
                    > C->S: RCPT TO: <invalid@...>
                    > S->C: rejected. recipient does not exist
                    > C->S: QUIT
                    >
                    > no message is exchanged here. your server does nothing after this. it
                    > does not send a bounce. If C is a normal MTA, it is its responsibility
                    > to generate a bounce, but this none of our business: we don't care.
                    >
                    > If on the other hand your server is misconfigured, it will accept the
                    > mail during the smtp transaction. then later it will find out that it
                    > cannot deliver the message. it will then generate a bounce and send it
                    > to the original sender. sometime ago, this was ok, but since a lot of
                    > spam uses forged addresses, such bounces go to innocent people who did
                    > not send anything. This is backscatter.
                    Ok, thanks for the explication! This will help me.


                    --
                    -Nicolas.
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