Prev: postfix as forwarder and backscatterer problem
Next: postfix as forwarder and backscatterer problem
From: Vasya Pupkin on 22 Jul 2010 10:36
I'm doing best I can to fight spam. What I described happens with spam
that pierced through all filters. There is no 100% way to detect spam
and you know that. So, some percentage will still go through and will
be forwarded, and possibly rejected, causing bounce to be generated.

On Thu, Jul 22, 2010 at 6:27 PM, Wietse Venema <wietse(a)porcupine.org> wrote:
> Vasya Pupkin:
>> Hello.
>>
>> First, I have spent two days reading articles and searching web for
>> solution but failed there. I am using postfix as an mx for my domains,
>> it accpets mail for different addresses withing my domains which is
>> then forwarded to other external domains, i.e. google.com and other
>> mail services. Mail for unknown users is rejected, many other check
>> are performed, but still sometimes my system acts as a backscatterer
>> when something like this happens:
>>
>> 1. Incoming mail passes all tests, it's coming to one of the addresses
>> within my domain, i.e. existing-user(a)mydomain.tld
>> 2. Postfix then forwards mail to external domain, i.e. myemail(a)mailservice.tld
>> 3. For some reason mailservice.tld rejects this mail, i.e. it doesn't
>> like it's content or size.
>> 4. Postfix then bounces mail to sender, which can be forged, and thus,
>> becoming a backscatterer.
>>
>> Is there any way to prevent postfix from sending bounces anywhere?
>
> The best conutermeasure is not to forward spam.
>
> The second-best solution requires the ability to predict if a
> specific message will be rejected down-stream. Let me know when
> you solve that, so I can add it to Postfix.
>
>        Wietse
>

From: Randy Ramsdell on 22 Jul 2010 10:45
Vasya Pupkin wrote:
> Hello.
>
> First, I have spent two days reading articles and searching web for
> solution but failed there. I am using postfix as an mx for my domains,
> it accpets mail for different addresses withing my domains which is
> then forwarded to other external domains, i.e. google.com and other
> mail services. Mail for unknown users is rejected, many other check
> are performed, but still sometimes my system acts as a backscatterer
> when something like this happens:
>
> 1. Incoming mail passes all tests, it's coming to one of the addresses
> within my domain, i.e. existing-user(a)mydomain.tld
> 2. Postfix then forwards mail to external domain, i.e. myemail(a)mailservice.tld
> 3. For some reason mailservice.tld rejects this mail, i.e. it doesn't
> like it's content or size.
> 4. Postfix then bounces mail to sender, which can be forged, and thus,
> becoming a backscatterer.
>
> Is there any way to prevent postfix from sending bounces anywhere?
>
I am dealing with the same thing. I have to forward to non-local mail
servers and I try to mimic some of those settings but we still get a few
that pass local mail to external mail which is then rejected.
Maybe a script that checks for the rejects and discards would work? I
will think through that approach for use here actually.

RCR
Linux System Administrator

From: Vasya Pupkin on 22 Jul 2010 10:51
I just got an idea to use smtp_header_checks to discard mail from
postmaster(a)mydomain.tld which is used for bounce emails. I hope it
will work.

On Thu, Jul 22, 2010 at 6:45 PM, Randy Ramsdell <rramsdell(a)activedg.com> wrote:
> Vasya Pupkin wrote:
>>
>> Hello.
>>
>> First, I have spent two days reading articles and searching web for
>> solution but failed there. I am using postfix as an mx for my domains,
>> it accpets mail for different addresses withing my domains which is
>> then forwarded to other external domains, i.e. google.com and other
>> mail services. Mail for unknown users is rejected, many other check
>> are performed, but still sometimes my system acts as a backscatterer
>> when something like this happens:
>>
>> 1. Incoming mail passes all tests, it's coming to one of the addresses
>> within my domain, i.e. existing-user(a)mydomain.tld
>> 2. Postfix then forwards mail to external domain, i.e.
>> myemail(a)mailservice.tld
>> 3. For some reason mailservice.tld rejects this mail, i.e. it doesn't
>> like it's content or size.
>> 4. Postfix then bounces mail to sender, which can be forged, and thus,
>> becoming a backscatterer.
>>
>> Is there any way to prevent postfix from sending bounces anywhere?
>>
>
> I am dealing with the same thing. I have to forward to non-local mail
> servers and I try to mimic some of those settings but we still get a few
> that pass local mail to external mail which is then rejected.
> Maybe a script that checks for the rejects and discards would work? I will
> think through that approach for use here actually.
>
> RCR
> Linux System Administrator
>
>

From: Vasya Pupkin on 22 Jul 2010 10:52
You of course understand that this is not possible, right?

On Thu, Jul 22, 2010 at 6:50 PM, Wietse Venema <wietse(a)porcupine.org> wrote:
> Vasya Pupkin:
>> I'm doing best I can to fight spam.
>
> Then you will have to predict what mail will be rejected down-stream.
> Let me know when you solve that problem :-)
>
>        Wietse
>
>> that pierced through all filters. There is no 100% way to detect spam
>> and you know that. So, some percentage will still go through and will
>> be forwarded, and possibly rejected, causing bounce to be generated.
>>
>> On Thu, Jul 22, 2010 at 6:27 PM, Wietse Venema <wietse(a)porcupine.org> wrote:
>> > Vasya Pupkin:
>> >> Hello.
>> >>
>> >> First, I have spent two days reading articles and searching web for
>> >> solution but failed there. I am using postfix as an mx for my domains,
>> >> it accpets mail for different addresses withing my domains which is
>> >> then forwarded to other external domains, i.e. google.com and other
>> >> mail services. Mail for unknown users is rejected, many other check
>> >> are performed, but still sometimes my system acts as a backscatterer
>> >> when something like this happens:
>> >>
>> >> 1. Incoming mail passes all tests, it's coming to one of the addresses
>> >> within my domain, i.e. existing-user(a)mydomain.tld
>> >> 2. Postfix then forwards mail to external domain, i.e. myemail(a)mailservice.tld
>> >> 3. For some reason mailservice.tld rejects this mail, i.e. it doesn't
>> >> like it's content or size.
>> >> 4. Postfix then bounces mail to sender, which can be forged, and thus,
>> >> becoming a backscatterer.
>> >>
>> >> Is there any way to prevent postfix from sending bounces anywhere?
>> >
>> > The best conutermeasure is not to forward spam.
>> >
>> > The second-best solution requires the ability to predict if a
>> > specific message will be rejected down-stream. Let me know when
>> > you solve that, so I can add it to Postfix.
>> >
>> > ? ? ? ?Wietse
>> >
>>
>
>

From: "N. Yaakov Ziskind" on 22 Jul 2010 11:17
In my experience, ALL the NDRs I've ever seen are useless - if mail is
bad, it should be REJECTed, otherwise the system is breaking down
somewhere.

Is there a way to just drop bounces on the floor?

Vasya Pupkin wrote (on Thu, Jul 22, 2010 at 06:52:22PM +0400):
> You of course understand that this is not possible, right?
>
> On Thu, Jul 22, 2010 at 6:50 PM, Wietse Venema <wietse(a)porcupine.org> wrote:
> > Vasya Pupkin:
> >> I'm doing best I can to fight spam.
> >
> > Then you will have to predict what mail will be rejected down-stream.
> > Let me know when you solve that problem :-)
> >
> > � � � �Wietse
> >
> >> that pierced through all filters. There is no 100% way to detect spam
> >> and you know that. So, some percentage will still go through and will
> >> be forwarded, and possibly rejected, causing bounce to be generated.
> >>
> >> On Thu, Jul 22, 2010 at 6:27 PM, Wietse Venema <wietse(a)porcupine.org> wrote:
> >> > Vasya Pupkin:
> >> >> Hello.
> >> >>
> >> >> First, I have spent two days reading articles and searching web for
> >> >> solution but failed there. I am using postfix as an mx for my domains,
> >> >> it accpets mail for different addresses withing my domains which is
> >> >> then forwarded to other external domains, i.e. google.com and other
> >> >> mail services. Mail for unknown users is rejected, many other check
> >> >> are performed, but still sometimes my system acts as a backscatterer
> >> >> when something like this happens:
> >> >>
> >> >> 1. Incoming mail passes all tests, it's coming to one of the addresses
> >> >> within my domain, i.e. existing-user(a)mydomain.tld
> >> >> 2. Postfix then forwards mail to external domain, i.e. myemail(a)mailservice.tld
> >> >> 3. For some reason mailservice.tld rejects this mail, i.e. it doesn't
> >> >> like it's content or size.
> >> >> 4. Postfix then bounces mail to sender, which can be forged, and thus,
> >> >> becoming a backscatterer.
> >> >>
> >> >> Is there any way to prevent postfix from sending bounces anywhere?
> >> >
> >> > The best conutermeasure is not to forward spam.
> >> >
> >> > The second-best solution requires the ability to predict if a
> >> > specific message will be rejected down-stream. Let me know when
> >> > you solve that, so I can add it to Postfix.
> >> >
> >> > ? ? ? ?Wietse
> >> >
> >>
> >
> >

--
_________________________________________
Nachman Yaakov Ziskind, FSPA, LLM awacs(a)ziskind.us
Attorney and Counselor-at-Law http://ziskind.us
Economic Group Pension Services http://egps.com
Actuaries and Employee Benefit Consultants

 |  Next  |  Last
Pages: 1 2 3 4
Prev: postfix as forwarder and backscatterer problem
Next: postfix as forwarder and backscatterer problem