sendmail greet_pause feature

[Alex Neuman van der Hans]

Try http://www.city-fan.org/ftp/contrib/mail/ and see if there's an RPM 
that'll fit your box.

Roger Jochem wrote:
> I'm using the rpm version of sendmail in my centos-3 box (sendmail 
> 8.12) and I would like to upgrade to sendmail 8.13 to use this 
> feature, that seems really great. Is there some problem I should be 
> aware, or the tar.gz version found at sendmail.org would work fine on 
> my machine? Anyone using 8.13 at centos-3 or some similar OS?
>
> Regards
>
> Roger Jochem
>
> ----- Original Message ----- From: "Anders Andersson, IT" 
> <anders.andersson at ltkalmar.se>
> To: "MailScanner discussion" <mailscanner at lists.mailscanner.info>
> Sent: Wednesday, February 01, 2006 8:01 AM
> Subject: RE: sendmail greet_pause feature
>
>
>>> -----Original Message-----
>>> From: mailscanner-bounces at lists.mailscanner.info
>>> [mailto:mailscanner-bounces at lists.mailscanner.info] On Behalf
>>> Of Jim Holland
>>> Sent: Wednesday, February 01, 2006 9:12 AM
>>> To: MailScanner mailing list
>>> Subject: OT: sendmail greet_pause feature
>>>
>>> Perhaps other sendmail users know all about this, but I have
>>> only looked at it for the first time.
>>>
>>> I run sendmail 8.13.1 and have decided to implement the
>>> greet_pause feature for the first time (after seeing that it
>>> is a default option in Debian installations).  This requires
>>> a specified delay after connection, which can be network
>>> specific, before a client system is allowed to send any SMTP
>>> commands.  Any client that breaks normal SMTP protocols by
>>> trying to force commands before receiving the go-ahead is
>>> immediately disconnected.  This seems to distinguish very
>>> successfully between genuine mailers and spammers/viruses
>>> that are not RFC-compliant.
>>>
>>> Using a 5 second delay I have found that the system has
>>> blocked over 3200 connections in the first 24 hours I used
>>> it.  The client systems were all typical of spammers, with
>>> adsl/ppp/dhcp/dialup/cable/cpe type hostnames or no PTR
>>> record at all.  I found only four systems in the blocked
>>> group that looked as if they were genuine.  On further
>>> investigation I found that earlier log records for some of
>>> those sites indicated behaviour typical of virus infections
>>> in any case.
>>
>> I second that, thoguh I raised mine to 25 sec just for the fun of it. I
>> started low but raised it by 5 sec eeverytime and its been running
>> smooth. So far no one complained and the ones we have a great
>> mailexchange with been added to acces list
>>
>> /Anders
>>
>>>
>>> To implement the feature:
>>>
>>> Add the following to the sendmail.mc file:
>>>
>>> FEATURE(`greet_pause', `5000')dnl 5 seconds
>>>
>>> Rebuild sendmail and restart MailScanner:
>>>
>>> m4 < sendmail.mc > sendmail.cf
>>> service MailScanner restart
>>>
>>> Then specific entries for client hostname, domain, IP address
>>> or subnet can be put in the access file:
>>>
>>> GreetPause:my.domain    0
>>> GreetPause:example.com  5000
>>> GreetPause:10.1.2       2000
>>> GreetPause:127.0.0.1    0
>>>
>>> Definitely worth a look I would say, as it blocks large
>>> numbers of spammers before they are allowed to send any data,
>>> with very low risk of blocking genuine systems.  It even
>>> seems to allow genuine mail from infected systems to be
>>> accepted while blocking viruses from those same systems
>>> before the DATA phase - as many viruses seem to behave rather
>>> impolitely :-)
>>>
>>> Regards
>>>
>>> Jim Holland
>>> System Administrator
>>> MANGO - Zimbabwe's non-profit e-mail service
>> -- 
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>

-- 

Alex Neuman van der Hans
N&K Technology Consultants
Tel. +507 214-9002 - http://nkpanama.com/