Steve,
Thanks for the followup detail. Curiously, the model of "additional"
processing you describe has also cropped up in the EDI community and is the
motivation for X.435. From the typical email standpoint, this definitely
is UA processing, rather than MTA, but from a more general view, the darn
thing sure looks just like a message router (albeit one that might use more
than the address). One suspects that one approach to improving large-scale
message processing is to do load-leveling by delivering into multiple
mailboxes, just like having the DNS give out different IP addresses for
host-based load-leveling.
But alas, I continue to distract from the PEM agenda...
Dave
+1 408 246 8253 (fax: +1 408 249 6205)