From: "Robert G. Brown" <rgb(_at_)phy(_dot_)duke(_dot_)edu>
...
If a message comes in incorrectly addressed, yes, it will bounce. It
should, shouldn't it? This has nothing to do with whether or not it is
spam or a virus or any other kind of message. If it is a bad thing, it
is a very fundamental bad thing...
...
If the envelope sender was forged as is common in spam, universal in
worms, and practically nonexistent in legitimate mail, then your bounce
will afflict third party's mailbox. My mailbox receives enough worm
bounces to make me say it is an awfully bad thing.
The only fix is to have your external MX servers know all valid
addresses and so reject junk before it can be accepted and later
need to be bounced. That fix is often impractical or impolitic.
No, SPF, RMX, TOES, etc. etc. etc. cannot fix this problem unless you
assume frictions (deployment resistence and delays) do not exist
or you discard SMTP design goals including transporting messages among
complete strangers.
People who know each other's crypto keys are not strangers.
If you could someday trust organizations to vouch for strangers and
not sell spam-for-a-day certs to Ralsky/Ricther/&co, then today you
could trust the same outfits to not sell spam-for-a-day/week/years IP
bandwidth accounts.
Vernon Schryver vjs(_at_)rhyolite(_dot_)com