2 (minor) points for potential discussion in Columbus

1) RFC 1421: 5.2.1.3; in the asymmetric key management case, version/expiration
subfield be the (binary) (tagged) ATN of 
X.509.AuthenticationFramework.SerialNumber
represented for inclusion in a transmitted header using the procedure defined
in Section 4.3.2.4 of RFC 1421 - rather than hex.

This would aid higher-quality interaction with other secured std telematic 
services.

I recognise this would mean a change to the Proposed Standard.

2) OIW X.499 SIG defines privacy-enhanced-mail an uninterpreted OCTET STRING via
an EXTENDED-BODY-PART-TYPE declaration. With MIME-PEM this needs to be updated 
to
permit MHS UAs to know to process the bodypart appropriately.

I recognise this is not for IETF. However, Rich Ankey ensures X.400 SIG and 
PEM-WG
liase suitably.