Re: [courier-users] breaking smtp

Gordon Messmer wrote:

> I was criticizing you because you asserted that greylisting was broken,
> and then defended the practice of transparently redirecting your users'
> connections. I meant to illustrate that because SMTP is abused such as
> it is, we all break it to make it more sane.
>
> When you said that "one was about breaking mail delivery for perfectly
> valid mail", I assumed that you were talking about greylisting, because
> you appeared to be replying to what I wrote. I disagree that SPF breaks
> valid mail, but that's immaterial to the point that I was making. My
> point was that when you redirect users' connections, it is you that is
> at fault when that mail is considered invalid because the user's SPF
> records indicate that your mail server isn't allowed to send his email.

Sure - but since the number of systems enforcing SPF on the receiving
end is thankfully negligible it's immaterial. Most proponents of SPF
seem to wave the flag of pretending to be doing something with it by
adding the relevant DNS records, while not enforcing the checking on
their inbound servers.

> SPF is incompatible with your configuration, but that doesn't mean that
> SPF is a broken specification.

Are your mail servers actually set up to bounce mail purely based on
SPF? If so, is it on a system handling mail for hundreds of thousands of
users across hundreds of thousands of domains? Do you have DNS control
of all of those domains?

The point is that unless _everybody_ adopts it, and more importantly -
enforces it (which won't happen), it's not going to work to a point
where it's useful.

You can't just come up with things that break SMTP unless it's
sufficiently backwards compatible to not break existing setups. It only
takes a handful of important users to complain before such measures get
disabled by decree from on a high. One typical example is using RBLs
that yield too many false postives [cough]SpamCop[/cough].

And at the end of the day, SPF just isn't all that effective anyway.
When you can reduce your spam influx by 2-3 orders of magnitude using
more sensible and cheaper methods, what is the point of bothering with
more questionable methods?

Gordan

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