[Gllug] spamassassin v bogofilter

Rich Walker rw at shadow.org.uk
Thu Jun 2 14:11:24 UTC 2005

Michael Moritz <mimo at gn.apc.org> writes:

> On Thursday 02 June 2005 14:43, Rich Walker wrote:
>> Michael Moritz <mimo at gn.apc.org> writes:
>> > On Thursday 02 June 2005 13:17, Jason Clifford wrote:
>> >> On Thu, 2 Jun 2005, Michael Moritz wrote:
>> >> > This is a misunderstanding. The receiving SMTP server (the one that
>> >> > does the greylisting) reads the MAIL FROM, RCPT TO, and client
>> >> > address, then checks the greylisting database and issues a 450. This
>> >> > is before the DATA section of the SMTP session.
>> >>
>> >> You are trusting that all other MTAs and MUAs do the "right thing".
>> >> Experience shows that this sometimes is not the case.
>> >
>> > What do you mean? My SMTP server disconnects after the greylist check,
>> > the session is ended. No way the sender can continue sending the mail
>> > data as the tcp session is closed.
>> The sender then drops the mail on the floor, or bounces it to the
>> originator with an unhelpful message.
> Thought this was about the reduction of mail server load, not weird MTA 
> implementations...

Well, losing mail going to the server will reduce the load, but not in a
way you want.

And any strategy for running an MTA unfortunately has to take on board
that not everyone is running a Real MTA - some of them appear to have
hired a Big Consulting Firm to write a "Mail System" for them to make
sure it's as f'd up as possible...

>> *This* is the problem with greylisting - critical upstream MTA's break
>> when presented with it.
> That is why you would whitelist them beforehand.

But you can't tell *until* you lose mail from them. And if it's, say, a
new customer, you might never know.

> BTW, there is still a problem with this. What does one of these "critical 
> upstream MTAs" do when it is confronted with a genuine 4xx message? Does it 
> just lose the message, seriously? I think that's even more worrying than 
> greylisting...

Good question. I suspect some just tell the user "can't send your mail
hah haaa!" and others say "try again later". Anyone know?

cheers, Rich.

rich walker         |  Shadow Robot Company | rw at shadow.org.uk
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