> The "proof is in the pudding" -- auto-delete can only automatically delete
> exact matches of subscribers (not forwarding addresses) when that bounce is
> in RFC821/2 format, and not some funky Mail User Agent format.

It's called DSN (Delivery Status Notification) format and is described
in RFCs 1891-4.  It's also sometimes called notary format, after the
name of the IETF working group that developed it.