[exim] DKIM and/or DomainKeys

Is anyone out there using DKIM and/or DomainKeys in either a signing
and/or verifying mode?

I am specifically trying to deal with yahoo.com mail/spam, but it seems
like yahoo.com's own domainkey policy is that they are still in testing
"t=y" and they don't sign all messages "o=~", so what is there to do? Do
I have this right or am I missing something? Another sender that does
DomainKeys is cisco.com, but it seems like cisco.com doesn't have a policy
record, no _domainkey.cisco.com ??

Any help or insight would be greatly appreciated.

Thanks,

Dan