For the purposes of fighting spam the following configuration would be
sufficient:
1) Alice's client generates self signed cert
2) Alice's client uses DNS srv to discover XKMS service for email zone
3) Alice's client registers certificate with XKMS service
4) Alice sends email to Bob
5) Bob's client looks up policy of Alice's DNS zone, it is always
authenticate
using S/MIME, no root key specified, XKMS service specified.
6) Bob checks that message is signed correctly
7) Bob retrieves Alice's self signed cert via XKMS locate
Has anyone here suggesting the use of certificates in fighting spam
done an S/MIME interoperability testing?