[Raw Msg Headers][Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: Greylisting (again)?

I should keep a closer eye on this list...

My knowledge of zmailer's internals is somewhat limited, so bear with me
if I say something dumb :)

Matti Aarnio <mea@nic.funet.fi> wrote:
> On Thu, Jul 22, 2004 at 12:40:12AM +0200, Mike Acar wrote:
> > Hi,
> > 
> > A friend of mine reports great success with greylisting and I see there
> > was some discussion of it around February, but no conclusion or ideas on
> > how to implement it with zmailer.
> > 
> > What's the status now? Any ideas?
> Implementing it in the smtpserver is trivialish affair, but it has
> radical adverserial effects in the outgoing queue processing.

But this impacts zmailer users who are trying to send mail to sites
which use greylisting, right? In other words, this problem is orthogonal
to implementing support for it in the smtpserver - if greylisting
becomes popular, zmailer's scheduling+smtp-ta behavior will have to be
adapted to it, regardless of whether or not zmailer users themselves
greylist incoming mail.

Now that I reread what I wrote I realize I took for granted that it was
clear that I want to greylist incoming mail (which perhaps it was, but
why not be explicit ;), rather than asking about the general state of
zmailer relative to greylisting.

> The scheduler/smtp-ta interaction is such that when something
> retries in the outgoing smtp protocol, the whole target queue
> retries.  This gets a bit more complicated, when the queue
> has more than 2 messages.  IF the first one goes thru, then
> a batch of messages up to "over-feed" limit will be queued
> to the transport agent, BUT if the first one retries, then
> no further messages are queued at that time, and entire target
> queue retries.

If I read this correctly then the scheduler's underlying assumption
(which greylisting breaks) is that once a target accepts a couple of
messages, it's willing to accept them all. So a few messages may go
through, but then one will hit the recipient MTA's greylist, get a
temporary failure, and the entire rest of that queue will go back to
waiting for the next attempt?

> The "target queue" means messages in queue to e.g.   smtp/example.com
> target, NOT all messages in the system.


> Changing the queue logic in the scheduler might make the grey-list
> thing workable with ZMailer,  but I have no good ideas of what that
> logic should be.

I haven't yet read the greylisting whitepaper (which I clearly should)
but from the descriptions I've read it seems like the only reasonable
thing to do is to be somewhat naieve and just try everything in the
queue destined for that host; some of the messages may be greylisted,
and they get requeued, but those which had previously been greylisted
will (presumably) be accepted this time around.

Am I misunderstanding or just plain missing anything?

| Mike Acar | mike@trolltech.com |
To unsubscribe from this list: send the line "unsubscribe zmailer" in
the body of a message to majordomo@nic.funet.fi