Martijn de Munnik schrieb:
> Hi all,
>
> Sometimes our mail server is 'under attack' and we get a lot of these
> entries in our log file:
>
> Aug 17 11:08:19 stevie.youngguns.nl postfix/smtpd[14890]: [ID 197553
> mail.info] NOQUEUE: reject: RCPT from unknown[212.22.199.165]: 450 4.1.8
> <indispensabl...@homepc>: Sender address rejected: Domain not found;
> from=<indispensabl...@homepc> to=<[email protected]>
> proto=ESMTP helo=<homepc>
>
> Normally we reject about 15 msgs/min but when such an attack happens it
> peaks to about 700 msgs/min. The error is returned to the sending mail
> (spam) server is 450 domain not found. Because a domain lookup could
> also be a temporary failure this is a temporary error returned.
>
> The 450 error triggers the spammer to retry sending the mail.
>
> The to address is an unknown user on my system so postfix could return a
> 550 error. How can I do this?
>
> I've attached postconf -n output in main.cf.
>
> --
>
> Martijn de Munnik
>
if you trust your dns servers ( additional you should use a local dns
cache at minimum )
you can change
unknown_address_reject_code = 550
in main.cf
reject_unknown_recipient_domain
Reject the request when Postfix is not final destination for the
recipient domain, and the RCPT TO domain has no DNS A or MX record, or
when it has a malformed MX record such as a record with a zero-length MX
hostname (Postfix version 2.3 and later).
The unknown_address_reject_code parameter specifies the numerical
response code for rejected requests (default: 450). The response is
always 450 in case of a temporary DNS error.
--
Best Regards
MfG Robert Schetterer
Germany/Munich/Bavaria
