John Levine wrote,
| The only way to diagnose these things is with list probes, messages sent to
| each subscriber with a code in the subject and body that identifies who you
| sent it to, so when a smashed NDR comes back you can figure out which message
| and hence which address it was.
There are some smashed (good term for it, John) NDRs that don't return body
or subject, so one has to put the probe identification into whatever it does
return. For each incident that requires a probe, you have to tailor the
probe to the particulars of the NDR.
I had a subscriber forwarding to a nonexistent address on Prodigy without the
courtesy to rewrite the envelope. All Prodigy's NDR said was that
com was not a valid account, no headers, body, or anything
from the original text, from the trip from the list host to the subscribed
address, nor from the trip from the subscribed address to Prodigy. It never
occurred to those people that the forwarding destination alone could possibly
be insufficient information.
The only clue was that at least Prodigy was returning to the envelope sender.
(That was the only part they did right, and when they implemented it that way
they probably congratulated themselves very lavishly.) Putting an identifier
into the body or the subject would not have helped. (Lacking VERP capability
then, I did something that's been posted here before and needn't be repeated,
but it wasn't pretty.)