From: Mitch Halmu [mailto:mitch@netside.net]
Sent: Thursday, May 24, 2001 2:48 PM
I will give you a solid reason why we won't try this, quoting
research
with POP-before-SMTP conducted by the founder of MAPS TSI,
Chip Rosenthal
http://users.laserlink.net/~chip/relay-pres-9910/
You don't have to believe me that our clients will not accept
that, take
his words instead:
"Our users hated it - particularly those using MS Outlook"
No need to describe what happens when your clients hate your
service...
On that same page, I found this very interesting. The part about false
positive, to normal relay testing, got my attention.
Guys, there are more cases that may look like an open relay, but really
aren't.
<quote>
Escalating Credentials
Curently deployed in Laser Link network
Amalgamation of two mechanisms:
POP-before-SMTP
Rate limiting
Count mail from originating IP address
...
Disadvantages:
Complex implementation
Will users accept upper limit?
False positive to conventional relay testing
</quote>
I don't see how you can have a false positive on an open relay test. Either
it allows you to send a test email through, or it doesn't. If it does,
it is by definition open.
Unless you mistakenly test a site that considers you to be a customer
and has specifically allowed relaying for you. But for somebody to
do that for ORBS, say, would be like calling them up and leaving a
voicemail saying "please block me, I dare you."
Usually, a false positive on a relay test can happen in one
of two ways:
1. you're downstream of the operators of the server
that you're testing, and therefore are legitimately
relaying through it (as you suggested), or
2. you don't wait to see if the message comes back.
Lemme expand on #2 just a bit. Some mail servers will appear
to accept all mail, and not send a 5xx response immediately.
Some won't even generate a bounce message. But they also won't
forward the message on to its' off-site recipient. It'll just
disappear into the bit bucket. That's not an open relay, but
most relay-tester scripts will just say "the message has been
accepted, it must be open."
Lemme expand on #2 just a bit. Some mail servers will appear
to accept all mail, and not send a 5xx response immediately.
Some won't even generate a bounce message. But they also won't
forward the message on to its' off-site recipient. It'll just
I created and run a couple of specialty mail servers that do just that. I
used to give the errors, and even tried to bounce back the mail to the
sender, but all we got then was a queue of undeliverable spam.
Spammers! Arghh!!