Re: [Exim] spam delay trick and smtp_accept_count patch.

On Mon, 2 Feb 2004, Giuliano Gavazzi wrote:

> let me take this slightly off subject.. Inspired by this idea I am
> now delaying for each message that scores points at our server,
> unless of course the score is over the upper limit (10 usually) in
> which case it is rejected with no delay.

This sounds as if you are inserting a delay at the DATA stage of the
SMTP transaction. I'd have to say that's not a good idea, and the
RFCs also say that one should minimise the delays during the DATA
stage in order to avoid various kinds of unpleasantness such as
duplicate deliveries.

The delays that I was discussing are applied at the RCPT stage, and
other folks have mentioned delays that can be applied even earlier,
such as at the HELO stage. Those seem OK to me. We inevitably also
have some delays at the DATA stage while spam-rating is done, but I
would not recommend inserting additional delays at that point.

We used to experience problems of sending MTAs retrying if we gave
them 5xx at end of data, but that problem seems to have been more or
less resolved now. If we ever did see such problems again, then the
cure is to blacklist them for rejection at an earlier stage, i.e most
likely the RCPT stage.