dccifd / greylisting problems

Mariano Absatz el.baby at GMAIL.COM
Tue Aug 3 16:08:25 IST 2004

On Mon, 2 Aug 2004 10:46:57 -0500, Smart,Dan <smartd at vmcmail.com> wrote:
> The negative of greylisting is that some "legit" mail servers may give up
> after one attempt.  These will need to be whitelisted to bypass greylisting.
> Also, there is a long discussion on DCC list on functionality, and it
> appears that an initial denial of 1 - 3 minute(s) is sufficient to stop most
> Spam senders, who send once then forget.  Most users would not see this
> delay.  Whitelisting will still be an issue for broken sites.
> Greylisting needs to run at the mail MTA, so that messages get blocked
> *before* they are accepted by your mail MTA.  That's the whole idea... Block
> messages once before accepting them the second time.
> Each message records a tuple in DCC:  The sender, recipient, and IP address
> of sending MTA.  After being saved the first time, every time this recorded
> tuple is seen, the message gets delivered immediately. The tuples have a
> time-to-live, and will expire off the DCC server eventually.
> <<Dan>>
> >  -----Original Message-----
> >  From: MailScanner mailing list
> >  [mailto:MAILSCANNER at JISCMAIL.AC.UK] On Behalf Of Matthew Henkler
> >  Sent: Saturday, July 31, 2004 10:03 PM
> >  Subject: Re: [MAILSCANNER] dccifd / greylisting problems
> >
> >  On Sat, 31 Jul 2004, John Rudd wrote:
> >
> >  > But I think it's more of a sendmail milter type thing than a
> >  > mailscanner thing.  By the time mailscanner sees the
> >  message, it's too
> >  > late to reject it for the sender to try again later.
> >
> >  Yes, that seems likely now that I think about it.  The way I
> >  have it set up at least, it is  most likely too late for
> >  MailScanner to do anything about.  Guess I'll have to play
> >  around with it at the MTA level.
> >
> >  Good explanation of greylisting for everyone though, thanks!
> >
Anyway... greylisting CAN NOT work within MailScanner. Graylisting has
to be done during the incoming SMTP dialog and must choose to accept
or temporarily reject (errcode 4XX) a given SMTP transaction.

MailScanner runs AFTER the SMTP transaction is over so there's no way
that you can do graylisting within it.

Maybe it could be implemented in a milter for sendmail, I dunno.

Mariano Absatz - El Baby
el (dot) baby (AT) gmail (dot) com
el (punto) baby (ARROBA:@) gmail (punto) com

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