X.400 Security

I've seen the claim that X.400 is more secure than SMTP many times.
The supporting evidence leaves me doubting.

Security features of X.400

Security standards related to X.400

• The ITSI DISA standard library pointed me to MIL-STD-2045-18500-1 AMHxn(D)-MHS-MSP, with the nice-sounding name "Message Security Protocol". According to Steve Kent, "MSP per se is capable of carrying any content type and has been profiled for carrying MIME, vanilla 822, and for being transported via MIME over SMTP". I haven't read it.
  You can fetch the docs (5 parts) in WP 5.1 format from the list here.
• PGP has been used by Maxware to provide security in an X.400 environment