I fixed ALL entries in the vpopmail DB that was wrong, still
Jun 9 18:07:30 mail send: delivery 3: deferral: Not_allowed_to_perform_deliveries_as_root./
Jun 9 18:07:30 mail send: status: local 0/10 remote 0/60
So i think the qmail-lspawn (see the source code, it has the error "Not_allowed_to_perform_deliveries_as_root")
is somehow unable to switch to correct user i think. (So it's root with uid 0, which is wrong)
Did you change any setuid in the last update or last 2-3 months?