Dear friend,

[Martin A. Brooks]

Oliver Gorwits wrote:
> True, I should have mentioned...
>
> DKIM (nee DomainKeys) probably has the most hope in my eyes, at
> least, but it's early days yet.
>
> http://www.dkim.org/

Many spammers were early adopters of SPF, DomainKeys etc.  There are 
some edge cases where they're useful for antispam filtering (i.e. for 
SPF where a domains sets "-all" and you get mail from an IP not listed 
in their record), but they're most certainly not antispam systems in 
their own right.