Re: Re: [spf-help] SRS for Exim

In <[email protected]> "Seth Goodman" <[email protected]> writes:

>> From: wayne
>> Sent: Thursday, April 29, 2004 4:59 PM
>
> <...>
>
>> BTFOOM why redirect is a modifier instead of a mechanism like
>> include.  They both change the SPF result.  Once upon a time, the
>> "all" mechanism was a modifier too.
>
> So for general understanding, what determines whether something should be a
> mechanism or a modifier?


Well, from the SPF spec section 3.2:

   There are two types of directives: mechanisms and modifiers.  A given
   mechanism type may always appear multiple times in a record.
   Modifiers may be constrained to appear at most once per record,
   depending on the definition of the modifier.  Unknown mechanisms
   cause processing to abort with the result "unknown".  Unknown
   modifiers are ignored by clients.


Now, the "all" mechanism is allowed to appear more than once because
it is a mechanism, but anything after the first all mechanism doesn't
do anything.  Modifiers may be constrainted to appear only once but,
as in the accred= modifier, it doesn't have to.

Mechanisms can have prefixes, modifiers can't.


-wayne