"Eric A. Hall" <ehall(_at_)ehsco(_dot_)com> writes:
If the reverse-path has been misconfigured to reference an inappropriate
mailbox (eg, list-request(_at_)domain) then this might even happen
automatically. This is *designed* to happen automatically with mailing
lists that use VERP and similar proposals:
| The VERP extension implements
| a way of automatically identifying undeliverable mail recipients,
| even when non-delivery reports originate from mail systems that do
| not implement delivery status notifications
VERP is basically dead for practical purposes.
At work, we run a small read-only mailing list which mainly targets
German IT workers. Apparently, many larger institutions gateway mail
from RFC 821/822 format to some X.400 derivate or proprietary mail
implementations, and these gateways throw away the distinction between
envelope address and header address.
As a result, even delivery failure notifications are regularly sent to
the address in the From: header, not just the regular stream of
out-of-office notifications during school vacations.
Even outside the list world, there are scenarios where sending to the
reverse-path is inappropriate. EG, when the Sender/From construct is
actually used, the notification is returned to the Sender instead of the
From parties.
At least one (not too popular) mail client puts unrouteable addresses
in Sender: fields if the user changes the From: address from the
default. :-(