I now agree with Jim's recommended addition of otherKeyId to
ReceipientIdentifier. I also agree with Paul that the S/MIME v3 Msg and
Cert specs already specify that X.509 Certs MUST be used in conjunction with
S/MIME msgs. In summary, I believe that it is appropriate for the CMS spec
to accommmodate non-X.509 certs, but S/MIME msgs MUST use X.509 certs.
J.G. Van Dyke & Associates, Inc.