This approach certainly isn't perfect :)
-----Original Message-----
From: Harald Alvestrand [mailto:Harald(_at_)Alvestrand(_dot_)no]
Sent: Tuesday, January 23, 2001 4:58 PM
To: Gwinn, Allen; ietf-822(_at_)imc(_dot_)org
Subject: Back-queries?
At 09:31 23/01/2001 -0600, Gwinn, Allen wrote:
This approach certainly isn't perfect. But simply opening a connection to
the sending host and checking RCPT TO:
<somewhere(_at_)your_own_domain(_dot_)whatever>,
looking for a 250 OK message before rejecting, then failing safe (i.e.
accepting anything where you can't connect to the host) might tend to slow
down a large hunk of spam.
hmm....I don't quite get how this would work out.
Let's consider a legitimate case: x(_at_)a sending mail to y(_at_)b
A->B: MAIL FROM x(_at_)a
B: (let's check if this is legit)
B->A: MAIL FROM legit-checker(_at_)b (intending to send RCPT TO x(_at_)a)
A: (let's check this)
A->B: MAIL FROM .......
it would definitely slow down things, yes.
Using null MAIL FROM when checking is one option.........if everyone allows
that. But then this is an open hole.
(I recently heard that one guiding principle of the Internet was the
question "what if EVERYONE did that?"....)
--
Harald Tveit Alvestrand, alvestrand(_at_)cisco(_dot_)com
+47 41 44 29 94
Personal email: Harald(_at_)Alvestrand(_dot_)no