watermarking and spam mail loops?

[Scott Silva]

Jeff A. Earickson spake the following on 8/30/2007 10:38 AM:
> Gang,
> 
> I'm trying to understand watermarking from the list archives
> (I took a month off the list), and I don't get it.  It looks
> like it might be useful for killing spam-caused mail loops
> between my front-end sendmail/MailScanner mail-relay and my
> backend local-delivery box.  The scene is:
> 
> 1) spammer with bogus return sends to a nonexistent Colby
>    email address.
> 2) if MailScanner doesn't kill it as spam, it gets relayed
>    onto the backend system, who doesn't know the recipient.
> 3)  the backend system is configured to send all non-local
>    email to the front-end box, who sees that it is supposed
>    to go to nonexistent Colby address, sent to the back-end,
>    return to step 2 until 26 hops have been hit.  Then drop
>    in postmaster's lap.
> 
> The summary of mail headers is below.  I notice that the 
> X-Colby-MailScanner-Watermark is different on every iteration.
> Can watermarking be used to kill this mail loop early on?
Snip...
There is a big minus to using the watermark. If you have users using Outlook 
or have an exchange server, the read receipts get marked as spam.

Shouldn't you have your frontend box do a recipient verify to the internal box 
and drop the mail to non-existent users? That way you drop the connection and 
don't have to worry about bounces.

-- 

MailScanner is like deodorant...
You hope everybody uses it, and
you notice quickly if they don't!!!!