[Mimedefang] Pre-Emptive Greylist entries

[Paul Murphy]

> Paul, I appreciate what you're saying above.  But isn't it likely that if
spammers
> are going to the trouble to add SPF records that they're also going to the
> trouble to retry after a tempfail, and thus defeat greylisting?

Yes, some are already doing this.  However, I suspect that others are now
smart enough to realise that anyone doing greylisting is probably also ahead
of the game on content filtering, so retrying is a waste of time.
Alternatively, they may be smart enough to realise that a "go away spammer"
response from a system they do get through to is unlikely to change if they
retry with a different address or similarly spammy content, so they may
update their lists to provide a smaller address database which has a much
higher confirmed delivery rate.  Business advantage and all that...

> The case that I was trying to check for was the case where the spammer
> sends through a proxy or a zombie and otherwise impersonates 
> the sender.

That's virtually impossible to check for, which leaves us with content
checking.

Paul.

-- 
No virus found in this outgoing message.
Checked by AVG Free Edition.
Version: 7.1.371 / Virus Database: 267.14.16/225 - Release Date: 09/01/2006