Preventing backscatter with sendmail

Pardon Blessings Maoneke blessings83 at
Thu Jan 22 10:24:59 GMT 2009

Is there a way of preventing backscatters on postfix. I have many
users and i am using postfix plus mysql database but there is a lot of
backscatters. How can i prevent such a scenario

On 1/21/09, Steve Freegard <steve.freegard at> wrote:
> Kai Schaetzl wrote:
>> Steve Freegard wrote on Wed, 21 Jan 2009 15:04:59 +0000:
>>>> I haven't followed this thread much, but would this work alongside or
>>>> instead of something like milter-null?
>>> It would work alongside milter-null, scam-backscatter is simply a
>>> recipient call-ahead milter.
>> e.g. it is meant to prevent *yourself* from creating backscatter not from
>> incoming backscatter. I think the name of this milter is rather confusing.
> Yes - I agree.
> I also suspect that due to the name - people will think of this milter
> as some sort of 'silver-bullet' to prevent backscatter emanating from
> their host which would be a bad assumption.
> Rejecting invalid recipients on a gateway machine is a good start; but
> the administrator has to actually make sure the back-end hosts that
> actually receive the call-aheads isn't accept-then-bounce (e.g. it
> accepts all the recipients and the entire message then sends a DSN after
> the message has been accepted - *cough*Exchange 5.5*cough*) as in this
> case this milter would be no help; in fact it would actually reduce the
> efficiency of the gateway as it would carry on doing call-aheads even if
> the back-end doesn't reject invalid recipients based upon the
> documentation (see milter-aheads 'is-blind-mx' tests for an example of
> how to do this right).
> Many domains mail servers do not reject invalid recipients correctly:
> [root at mail ~]# ./
> Found 382 domains; pass=4 (1.05%), fail=378 (98.95%)
> pass = servers that reject invalid recipients
> fail = servers that accept all recipients
> Note that the 'fail' statistics could also count domains with
> 'catch-all' accounts.
> Regards,
> Steve.
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Pardon Blessings Maoneke

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