Stealth Blocking

J.D. Falk jdfalk at
Sat May 26 03:24:59 UTC 2001

On 05/25/01, Shawn McMahon <smcmahon at> wrote: 

> On Thu, May 24, 2001 at 05:49:54PM -0700, Roeland Meyer wrote:
> > 
> > Guys, there are more cases that may look like an open relay, but really
> > aren't.
> 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.

	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."

J.D. Falk                                                SILENCE IS FOO!
<jdfalk at>

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