I apparently forgot to reply back in March. Sorry.
Spencer Dawkins <spencer@xxxxxxxxxxxxx>
I was thinking about this from the client's perspective (if the collation
doesn't report "error", how does the client know to report anything to
someone who might be able to fix the input?).
There's no point in doing that. Take my home, IMAP. If an IMAP client
tells the server to sort the messages by subject, and one message's
subject contains an illegal ISO-2022-JP sequence, the collation will
return "error" a few times. That's not a bug in the client or server,
it's just another broken mail message. Usually it's spam. Routine.