Re: SMTP Scans

From: Kurt Seifried <bt(at)seifried.org>
Date: Thu Apr 24 2003 - 15:43:20 EDT

> >>For the last few months our ISP (BT) has apparently been scanning our
> >>mail servers for open relays, this is happening up to
> >>12 times a day across both Primary & Secondary mail servers.
> >
> >I don't condone this, but this is fairly common practice amongst UK ISPs.
> >
> >Regards,
> >
> >
> >Mally Mclane
> >RIPE NCC - Operations
>
> Why the aggressive schedule? For your "commercial" (as in - not end

Daily scans = up to 24 hours of spam email. Weekly scans = up to 168 hours of spam email. Scans every 2 hours = a LOT less spam email sent through an open relay. We're talking broadband here, a lot of email can be sent if the server is pumping it flat out for a day or a week or a month. Remember that the threat model here mostly consists of customers setting up a new server as an open relay, or accidently configuring an existing system as an open relay (witness the thread on upgrading exchange and opening up relaying).

Or to put it this way: why do you think earthlink, aol and a LOT of spam packages label email from cablemodem, dsl and other broadband network blocks as spam? Hint: it has to do with all the spam coming from them.

Kurt Seifried, kurt@seifried.org
A15B BEE5 B391 B9AD B0EF
AEB0 AD63 0B4E AD56 E574
http://seifried.org/security/

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Received on Fri Apr 25 14:39:27 2003