Neil Brown wrote:
What am I missing?
NeilBrown
I agree that extensibility *is not* an issue
The reason being, the exists: method allows arbitrary
function to be built into the server that is serving the
domain that the exists queries are being asked about.
The exists: macro language ("domain specifiers") contains
expandables for all information known at MAIL FROM: time.
To extend SPF any more would mean a "modularity violation"
where the extension would be violating the interfaces of
the layers above and below it.