No, the email never arrives. The rejection message comes from the
spammer's SMTP or server. You do not use your bandwidth to send the
mail
back because the mail never arrives. The connection is refused
before
the server can send the mail during the handshake.
I stand corrected on the bandwidth savings. But, I still like
Spam Assassin better because it catches so much more spam.
I still disagree as it doesn't stop any spam. It just hides it. Maybe it
should be called "Spamdelusion" instead of Spamassassin as it deludes
you into thinking you're getting less spam when all you're doing is
either hiding it or tagging it. To be an "assassin" it would actually do
something to stop the spam.
If every user actually used the tagged spam to report the spammers, or
examine the headers to block the sender IP, which is probably a rogue
ISP or an open relay, then it might actually stop some spam.