Mail being sent from my domain...

[RW]

On Sat, 06 Jan 2007 14:33:46 +0000
Matthew Seaman <m.seaman at infracaninophile.co.uk> wrote:

> Your reasoning is incorrect.  The presence or absence of SPF records
> affects how the systems that are the targets of the spam attack work,
> and those are not in the control of the spammers.  The ability of
> a mail system to realise by analysis of SPF records that the mailer
> connecting to it is an impostor that has no right to send mail from
> the falsely claimed sender address means that the message can be
> rejected early during the SMTP dialogue with a 5xx error (ie
> permanent delivery failure) even before the body of the message has
> been transmitted. 
> ...
> Secondly, you are assuming that the software the spammers use to
> inject e-mail is compliant with the various standards (RFCs 2821,
> ...

Delivery failures are normally generated by the sending server. If you
block SPF failures at the SMTP level there  are two possibilities. If
the sender is a real MTA it will generate a backscatter delivery
failure. If it's a spambot or spamming script then it wont, but it
wouldn't have anyway, with or without SPF. 

SPF may help fight spam, but I don't see how it can have a major impact
on backscatter when people use 5xx errors.