Greylisting and new posters

Mel Flynn mel.flynn+fbsd.questions at
Sat May 30 11:23:46 UTC 2009

On Saturday 30 May 2009 10:20:06 Erik Norgaard wrote:
> Mel Flynn wrote:
> > Is it possible to:
> > a) Put a big-red-blink-popup-attentiongrabbing monster text into the
> > subscription page about first posts being delayed with a link to
> > greylisting? b) Hash the bodies of greylisted messages and reject /
> > discard if the same body with a different msg id is being received?
> >
> > I'd be happy to contribute to b) if it is thought that the incoming
> > mailer can handle the hashing and storage of this information.
> Hi, ok sorry about that mail yesterday :) I've been off the list for
> some time.

Don't be. It's been bothering me for a while and you weren't even the trigger. 
Ironically the trigger was the endless and rather pointless discussions about 
list moderation.
The thing with double posts like these is that they are more frequent as of 
late and sometimes lead to 2 seperate threads about the same thing, where I 
already have half a reply ready only to notice that it was already covered "in 
the other one".

<snip information>

> Your option b) won't work: you propose to reply with a 2XX (OK) or 5XX
> (rejected, don't try again) if subscriber sends the message again.
> Problem is that the server after receiving the 450 error will retry
> after some time and this may be before the sender is white listed. So if
> you implement the solution you propose you risk that the original
> message is either discarded or rejected.

Not unless the retrying mailer is really broken.

> So, you need to come up with an idea of how to distinguish between the
> server resending the same message and the subscriber resending the same
> message. If anything, I believe it's most likely that the subscriber
> will not send the exact same message, missing some blanks or double
> signature line etc...

Most of the time it's identical, but I haven't investigated white-space 
differences. And like I mentioned in the original email, the msg id is the 
identifier. md5(body) as key generates msg-id foo, this message has msg-id 
bar, so redirect bar to /dev/null. Once foo delivered delete from state table.

> Question: Did grey listing actually reduce the amount of spam on the
> list? I eventually dumped it as it caused more problems than it solved.

It does marginally for me, for the list I have no idea. It seems to be more 
effective with viruses then "professional spam".

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