[MAILSCANNER] Reverse NDR attack.How to combat ? Any ideas ?

[Glenn Steen]

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On 21/09/05, Douglas Ward <binaryflow at gmail.com> wrote:
> I am using a postfix/MailScanner combination on our e-mail gateways.  We use
> the relay_domain and relay_recipient options to only allow mail through if
> it is first a valid domain and second if it is a valid recipient on the
> domain.  It is a bit of manual work to keep the recipient list up to date
> but they tell me pretty quickly if I forget!  :)  With this setup postfix
> automatically rejects the message.  I don't see many NDR's in the queue
> waiting to be processed.  I figure its either that I haven't been dictionary
> attacked yet or postfix is doing a good job!
>
Very likely that Postfix is doing its job well!
I imagine you've looked at
http://wiki.mailscanner.info/doku.php?id=documentation:configuration:mta:postfix:how_to:reject_non_existent_users#rejecting_unknown_non-local_users
and
http://www-personal.umich.edu/~malth/gaptuning/postfix/ for some
examples of nice scripts that remove the need for "manual
intervention"... If you're using a "non-local" server which present
it's userbase/mailboxes via LDAP, at least.
It's also fairly simple to script something around ldapsearch (I had
already done that when I saw this info the first time:). Run from
cron, this makes it so the M-Sexchange admin can do whatever he likes,
postfix will know about it within X minutes (15 in my case).

--
-- Glenn
email: glenn < dot > steen < at > gmail < dot > com
work: glenn < dot > steen < at > ap1 < dot > se

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