On Tue, 11 May 2004, Tony Finch wrote:
It turns out that conditionals are not the problem: the exists mechanism
combined with wildcard DNS records is enough. The crucial limitation is in
the macro language, which is only slightly too weak.
I should have noted that because SPF doesn't allow you to chop parts off a
domain name one at a time, it is also too weak for less powerful models of
computation than the Turing machine. i.e. I believe you also cannot
implement a pushdown automaton or a finite state automaton.
--
Tony Finch <dot(_at_)dotat(_dot_)at> http://dotat.at/