Hi,
I haven’t worked with NAESB so far, so maybe I do not fully understand your problem. But here are my thoughts:
S/MIME encryption is part of AS2 standard. If so, what you are trying to achieve is sending mime message with only some payload encrypted using PGP, right? In this case encrypt attachment or body of mime using pgp, add it to properly constructed mime message and send as unencrypted AS2 message. Then you get AS2 advanatages (http transfer protocol, mdns, etc) and your partner can decrypt attachment/body of message using pgp.
#Flow-and-Java-services#webMethods#Integration-Server-and-ESB