>From: "Alan J. Flavell" <flavell@???>
>To: "Kevin P. Fleming" <kpfleming@???>
>cc: Exim users list <exim-users@???>
>Subject: Re: [Exim] Idea to slow down spammers
> <mailto:exim-users-request@exim.org?subject=unsubscribe>
>Date: Wed, 30 Apr 2003 13:01:07 +0100 (BST)
...
>Another point. The dictionary scanners whose behaviour I had been
>watching would still start a fresh series of probes on-schedule (at
>intervals of typically 20-30 minutes) even if we were still delaying
>our response to their previous series, so I'm a bit concerned that if
>we took this too far, we might be setting ourselves up for a
>denial-of-service attack.
You can try to guard against this by setting
smtp_accept_max_per_host to a reasonably small value in the main
configuration section. I do this here. It can also help to contain
"bursty" mailing list fanout hitting your servers. In particular
EZLM (qmail) mailing lists tend to do this as they use VERP. So
each message arrives with just one recipient.
