Author: Alan J. Flavell Date: To: Dave C. CC: Exim users list Subject: Re: [Exim] How to force SMTP AUTH for certain return-path ?
Well, I'm not the original poster of this thread, but it's a scenario
that I recognise only too well...
On Mon, 24 Jun 2002, Dave C. wrote:
> Unless you are an open relay, spammers (who arent your customers)
> shouldnt be able to send mail through your server anyway.
Correct, but this isn't the problem. The spammers are spamming _our_
users, they aren't relaying through us.
> If you are trying to stop just spam coming TO your domain, which also
> forges a sender address in your domain, this might have some limited
> use. But surely not a very high percentage of the spam you receive falls
> into that category.
A nontrivial proportion of the spam that gets past the other defences
does indeed utilise the trick of counterfeiting a local user as the
envelope sender.
And if the spam-rating or anti-virus checks are triggered (this is
exim v3 with a system_filter), the result (if no further logic is
used) is to bounce the mail to the envelope sender: in other words,
the mailer's defence mechanism in this case results in an intended
_victim_ getting the item anyway (as has been discussed here before).
> If a spammer wants to forge sender addresses in your domain name, there
> is currently no technical way to stop them from doing so, using servers
> which are not yours - only legal after-the-fact methods (eg, sue them
> for forgery)
