[exim] MARID, SPF, DomainKeys, SenderID ?

Hello,



Could somebody kindly summarize the MARID, SPF, DomainKeys, SenderID,
<whatever>?

Though some information can be searched through archives, it's still
hard to understand what technology to expect as a de-facto standard for
the near future.



As I can see, SPF is considered broken, SenderID is M$-specific and
Domain Keys (sponsored by Yahoo!) is expected to be the most appropriate
Open Source animal with Exim.



I still don't see the advantages/disadvantages from a, eh,
small-to-medium installation's point of view.



Does it mean Exim will have intrinsic Domain Keys support, like DNSBL
(formerly RBL)?

Should one expect that Domain Keys will be wide-spread?



Thanks.