I'll update http://www.mozilla.org/mailnews/arch/index.html to point to some documents about how the S/MIME extension was implemented.
see http://www.mozilla.org/mailnews/arch/index.html:
Misc
- S/MIME, PGP,
and where to start if you wanted to add PGP supports
- [old and out of date] notes for MIME & Compose plugins (PGP, S/MIME)
- [old and out of date] log for #mozmail, concerning PGP in Mozilla (5-23-2001)
-Seth
