I think it is quite clear that this is a syntax error, which causes
PermError.
Maybe for the "redirect=" modifier. But I would not be so intolerant and
return "PermError" if there are more than one "exp=" modifiers. I would
ignore any error that may happen when processing the "exp=" modifier.
I tend to see this problem from the developer's viewpoint. I admit
that the last version of the SPF proposal I reviewed in depth was
draft-ietf-marid-protocol-00 which clearly specified "exp" as global
and singular with the sole purpose of providing human-readable
explanation for the upstream and that I why I thought that SPF
implementations must not accept multiple "exp" modifiers.
It still remains a question however what SPF implementations should do
with multiple "exp" modifiers - use the first one found left to right
or evaluate all and concatenate the results?
Peter Karsai