OT - Greylisting

Julian Field MailScanner at ecs.soton.ac.uk
Fri Aug 11 12:20:37 IST 2006

Hash: SHA1

Jim Holland wrote:
> On Thu, 10 Aug 2006, Julian Field wrote:
>> The solution to this that I have just deployed here is "greylisting". I
>> have set the delay time to 10 minutes, and the whitelist-remember time
>> to 32 days. No-one notices the 10 minutes delay on the first email in a
>> conversation, and 32 days means that the monthly email reminder messages
>> from mailing lists are whitelisted.
>> My users are *really* fussy, and I ran a trial of greylisting for a week
>> with a few selected users who opted in to the trial. I purposely didn't
>> tell them what I was changing so I could run a proper blind test. Not
>> one of them noticed the 10 minute delay time. So I have just deployed it
>> out to all 2000 users I have, and there have been no complaints at all.
> I am puzzled to hear this, because the 10 minute delay time is set on your
> side - ie the delay time between connection attempts before your server
> will accept the connection.  However it doesn't take into consideration
> the problem of the delay that will occur on the sending side between
> delivery attempts.  Many systems will retry delivery only after a fairly
> long interval.  The default for sendmail is 30 minutes, but some busy
> systems will have a default of as long as 4 hours.  This means that in 
> practice I would expect the real delay to be far longer than 10 minutes 
> for many messages.
> Worse still, there are some systems that will treat a 451 error as a fatal
> error, and will not retry the mail.  I have found this with Yahoo and
> Gmail, for example.  (I was trying to force them to deliver to our
> secondary MX that has more bandwidth than we do because of their very
> annoying failure to implement the ESTMP "size" extension - meaning that we
> sometimes have to accept say 10 MB of traffic before we can then tell them
> that the message is too large.)
There is a list of the known large sites that suffer this problem, you 
just put it in your greylist.conf file. The milter-greylist package 
comes with it already inserted for you.


> Another concern is the impact that greylisting would have on the Internet 
> if its adoption became widespread - it would mean that all mail servers 
> would have to work twice as hard to deliver mail.  I do find the delivery 
> delays rather annoying as a sender of mail - seeing mail stuck in the mail 
> queue waiting for some possibly unknown period of time before it gets 
> accepted.
I agree with you. But in practice no-one appears to notice. After all, 
how many people sit there tail-ing their outgoing mail logs?
> That said, I am sure that greylisting does make a big impact on spam for
> those that implement it.
It certainly does.

I quite agree that there are various aspects of greylisting with which I 
am not entirely happy, but the advantages for my users outweigh them 
substantially. My management, who are not PHB's at all, agree with me. I 
am in the lucky position of having bosses who I respect :-)

>> It has got rid of the single-image stock adverts completely. :-)
>> Daniel Maher wrote:
>>> I've noticed that a lot of the image spam uses bitmap (.bmp) images.  Unfortunately, that SARE plugin appears to handle gif, png, and jpg images only.  Does anybody know of a plugin that will recognise bmp's as well?
>>> --
>>>   _
>>>  °v°  Daniel Maher
>>> /(_)\ Administrateur Système Unix
>>>  ^ ^  Unix System Administrator
>>> Sentio aliquos togatos contra me conspirare.
>>>> -----Original Message-----
>>>> From: mailscanner-bounces at lists.mailscanner.info [mailto:mailscanner-
>>>> bounces at lists.mailscanner.info] On Behalf Of Michele Neylon::
>>>> Blacknight.ie
>>>> Sent: August 7, 2006 9:53 AM
>>>> To: MailScanner discussion
>>>> Subject: Re: gOCR SpamAssassin plugin
>>>> The one that Dallas posted on the SA users group seems to work well:
>>>> http://www.rulesemporium.com/plugins.htm#imageinfo
>>>> --
>>>> Mr Michele Neylon
>>>> Blacknight Solutions
>>>> Quality Business Hosting & Colocation
>>>> http://www.blacknight.ie/
>>>> Tel. 1850 927 280
>>>> Intl. +353 (0) 59  9183072
>>>> Direct Dial: +353 (0)59 9183090
>>>> Fax. +353 (0) 59  9164239
>>>> --
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>>>> Support MailScanner development - buy the book off the website!
>> - -- 
>> Julian Field
>> www.MailScanner.info
>> Buy the MailScanner book at www.MailScanner.info/store
>> MailScanner customisation, or any advanced system administration help?
>> Contact me at Jules at MailScanner.biz
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- -- 
Julian Field
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