Stopping backscatter with D_REJECT

[Todd D. Taft]

I was hoping to avoid dropping messages on the floor for well-behaved 
servers.  While it's rare, I have found the occasional ham that gets 
marked as spam.  With D_REJECT, at least the sender gets a notification 
that the message didn't go through.  In looking at the logs, I think the 
backscatter messages are generated when the spammer disconnects the 
session immediately after ending the DATA part of the SMTP session but 
before the system responds with a reject code.  A legitimate MTA should 
wait for a reply.  Ideally, I'd like to try to reject, and only drop if 
the reject fails.

--Todd


On 4/14/17 6:22 AM, Robert Moskowitz wrote:
>
>
> On 04/14/2017 04:35 AM, Todd D. Taft wrote:
>> I'm running amavisd-new on a CentOS 7 system with postfix as my MTA.
>>
>> I've got amavisd-new set up to run as a pre-queue test in the 
>> postfix's master.cf:
>> smtp      inet  n       -       n       -       -       smtpd
>>  -o smtpd_sasl_auth_enable=yes
>>  -o receive_override_options=no_address_mappings
>>  -o content_filter=smtp-amavis:127.0.0.1:10024
>>  -o smtpd_tls_security_level=may
>> smtp-amavis  unix  -    -       y       -       2 smtp
>>  -o smtp_data_done_timeout=1200
>>  -o disable_dns_lookups=yes
>>  -o smtp_send_xforward_command=yes
>>
>> In my amavisd.conf, I've got it set to reject everything bad:
>> $final_virus_destiny = D_REJECT;
>> $final_banned_destiny     = D_REJECT;
>> $final_spam_destiny = D_REJECT;
>> $final_bad_header_destiny = D_REJECT;
>>
>> However, I've noticed that somehow I'm still generating some 
>> backscatter on this server.  (mails from local MAILER-DAEMON going 
>> out to alleged spam senders).
>>
>> Is there a way to stop this?
>>
> I use:
>
> $final_banned_destiny = D_DISCARD;
>
>
>

-- 
Todd D. Taft
taft at unclet.net

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