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List:       amavis-user
Subject:    Re: [AMaViS-user] greylist mails with score between 5 and 10?
From:       Tomasz Chmielewski <mangoo () wpkg ! org>
Date:       2007-04-17 18:40:30
Message-ID: 4625149E.2030300 () wpkg ! org
[Download RAW message or body]

Gary V schrieb:

(...)

> If used as an after-queue filter it's simply too late in the process.
> As far as Postfix is concerned it has accepted the message and is now
> responsible for it. Even if amavisd-new D_REJECTs it at this point
> Postfix would be obligated to create a bounce notice. This is just what
> you are trying to avoid (and is an argument for the use of D_DISCARD
> for spam and viruses). It's actually an argument for using amavisd-new
> as a before-queue filter but as we have discussed, doing so is not
> recommended or supported.

Of course, before-queue filtering will only work properly if we have 
enough processing power available to filter the mails before the SMTP 
connection times out.


Greylisting we know today has many advantages:
- it makes lot of spam not delivered
- as a result, it offloads mail/filter servers from content filtering

It has a big disadvantage: it introduces delay in mail delivery.


As I checked my mail server's stats, with greylisting applied to each 
and every incoming message, the delay ranged from few minutes to several 
days(!), with median being a couple of hours.

For someone using mail as a mean of discussion with lots of (often new) 
people, it's just unacceptable.


That's why "selective greylisting" was introduced. I personally use 
maRBL for selective greylisting - as I mentioned before, I greylist only 
mail sent from Windows machines, and that with sender address on RBLs.


This leads me to a conclusion that greylisting of mail with certain 
characteristics (aka "this mail is spam, but maybe is not spam" - points 
between 5 and 10) would make a lot of sense.

Of course it would be only useful when:
- we do selective greylisting, and
- we do before-queue content filtering


-- 
Tomasz Chmielewski
http://wpkg.org

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