[CentOS] Sendmail SMTP Brute-Force Attack

Fri Jun 15 16:49:27 UTC 2012
Les Mikesell <lesmikesell at gmail.com>

On Fri, Jun 15, 2012 at 11:25 AM, Shiv. Nath
<prabhpal at digital-infotech.net> wrote:
> >>
>> I need help for STOP this spamers right now.
>> Thanks in advance to anyone who can guide me

> i trust this helps, there is another solution but you do not use Postfix.

Sendmail is nearly infinitely configurable - and not all that
complicated if you do it in sendmail.mc instead of .cf.   But, the
really quick fix is to drop in a couple of milters.  milter-greylist
is in the rpmforge repo and will tempfail everything the first time it
sees a new sender (exceptions/timing configurable, of course).  Most
spammers don't retry, all real mail servers do, so at the expense of
an occasional delivery delay you avoid most of the problem.
MimeDefang is in both EPEL and rpmforge.  It lets you control most
sendmail operations in a small snipped of perl and allows you to run
any tests you want, including rbls and spamassassin before the message
is accepted at the smtp level.   MimeDefang is flexible enough that
you could add your own greylisting there, but it isn't included out of
the box (but the author has a commercial solution that is more

   Les Mikesell
      lesmikesell at gmail.com